xiii.Organic loading rate (OLR)

The OLR is the rate at which organic matter is added to the digester volume in relation to either time or the substrate's biological conversion capacity. The organic loading rate is directly promotional to the quantity of volatile solids loaded in the digester and hence it influences the biogas yield, with more methane production for lesser the OLR. If the reactor has higher concentration VFA's, then it implies that it is overloaded [101]. The loading rate of a digester is the daily volume of volatile solids given to the digester, and methane production are favorable with high loading rates [33].

xiv.Biological oxygen demand (BOD) and chemical oxygen demand (COD):

*The BOD and the COD affect biogas production too. The biochemical* oxygen demand determines the amount of oxygen needed by the microbes to decompose the substrate. If the BOD is high, then a more rapid organic degradation is achieved which leads to more biogas production. The COD measures all organic and inorganic biodegradable matter in feedstock or substrate. The value of COD of an organic waste helps predict the theoretical methane yield from the substrate. From experiments, if 0.5 l/gm of COD is removed, the approximate methane production is about 0.35 l/g [101, 111].

#### **2.6 Energy requirements for biogas process**

The production of biogas necessitates the addition of heat to keep the substrate at an appropriate temperature and the constant stirring of the substrate, either by hand or with an electric motor-driven stirrer [99].

Therefore, process heat energy requirement is determined by the relation in Eq. (3)

$$Q\_t = M \ast C \ast \left(T\_2 - T\_1\right) \tag{3}$$

where

Qt = Overall heat required to heat the slurry in Kilojoule (KJ);

M = Mass of the slurry in (Kg);

C = The specific heat capacity of slurry and is expressed in KJ/Kg°C.;

T2 = Desired digester slurry temperature in °C;

T1 = Temperature of the digester charge/slurry in °C,

M = Digester size (V) in m3 × density of slurry (ρ) Kg/m3 ; Density of slurry (ρ) = (Density of water + substrate density dung)/2; Specific heat of slurry = (specific heat of water (4.2KJ/Kg°C) + specific heat of the substrate e.g., cow dung (2.8KJ/ Kg°C)/2 = 3.5 Kg/Kg°C.

The digestor effluent contains waste heat that can be recovered and used to produce the necessary heat energy. The slurry's input temperature may rise by a few degrees Celsius as a result. This results in a potential 50% reduction in the total heat required by thermophilic digesters [31, 112]. External heating is most effective for digesters of a large or medium size and requires approximately twice as energy intensive as central heating. A total of 850–1000 W/m2 K−1 is the typical range for space heating, and 300–400 W/m2 K−1 is the typical range for space cooling [112].

Parameters such as microbe species, feedstock pretreatment, and biogas purification processes, substrate composition, substrate properties, and ideal reactor conditions must be managed to produce biogas profitably. Further investigation is required and have been actively a high interest area toward the enhancement of biogas production and biogas utilization through the application of engineering, biology/biotechnology, and technical innovations in order to achieve cost-effective biogas production [10, 113].


**Thermochemical Route for Extraction and Recycling of Critical, Strategic and High-Value Elements from By-Products and End-of-Life Materials, Part II: Processing in Presence of Halogenated Atmosphere**

**Ndue Kanari 1,\*, Eric Allain 1, Seit Shallari 2, Frédéric Diot 1, Sébastien Diliberto 3, Fabrice Patisson 3 and Jacques Yvon 1**

Received: 16 July 2020; Accepted: 18 September 2020; Published: 21 September 2020

**Abstract:** During the treatment of copper anode slime (CAS) under an air atmosphere, several aspects of the interactions of its main components (CuAgSe, Cu2−xSeyS1−y, Ag3AuSe2) with oxygen were described in Part I. As a comparative and complementary study, this work deals with the thermal behavior of CAS under air in the presence of polyvinyl chloride (PVC) between 195 and 770 ◦C. The preliminary thermal treatment of an e-waste sample containing brominated substances was also performed. The reaction products were systematically analyzed by scanning electron microscopy through energy-dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD) to investigate the thermal behaviors of the studied samples in a halogenated medium. At low temperatures, the copper, silver and selenium compounds of the CAS reacted with the HCl, issued from PVC degradation, leading to the formation of their respective chlorides. Bromides of valuable metals (Cu, Pb, Sn ... ) were synthesized during the e-waste treatment at 500 ◦C and they were distributed between the solid residue and gaseous phase. The data obtained give an insight into the reactivity of several metals towards halogenated substances, which may be valuable information for conducting the extraction and recycling of targeted elements from industrial by-products and end-of-life materials by a thermochemical route.

**Keywords:** critical and strategic materials; valuable metals; copper anode slime; PVC; de-chlorination; e-waste; thermal treatment; halogenation; metal halide volatilization

#### **1. Introduction**

The results described in Part I [1] of this investigation combined with research works cited therein [2–16] gave a general view of needs and secondary sources for a large range of materials, identified frequently as critical and strategic materials, and they are indispensable for present and forthcoming innovations in renewable energies, transportation and cutting-edge technologies.

These materials, mostly metals, are often concentrated in the by- and/or co-products of base metals extraction and they are subsequently separated and recovered employing pyro-and/or hydrometallurgical processes. It is expected that the actual and future demand for several of these materials will grow strongly, especially to feed the production of electric and electronic devices, while the lifespans of many products such as computers and cell phones are decreasing rapidly [4].

This trend, among others, leads to the generation of a huge waste stream (electrical waste and electronic equipment, WEEE), often designated as e-waste [5–8]. Its elevated content in high added value elements (precious, strategic, critical, rare and rare earths elements), particularly for "smart parts", makes this waste stream, a very attractive "urban mine" for the extraction of these components. But, it is necessary to emphasize that the hidden side of the e-waste stream is not all golden. These materials are composed on average of about 35% of metals, 35% of refractory oxides and ceramics and 30% of various plastics and resins. In addition to the complexity and miniaturization of the targeted metals which make their recovery difficult, the presence of chlorinated and bromated substances associated with plastics and many other components poses serious environmental problems during the recycling of e-waste. With appreciated functional properties, one of these plastics, polyvinyl chloride (PVC) is used in a broad range of products including electric and electronic appliances. With about 57% Cl (in pure PVC), it is an inherently fire-resistant plastic. However, the end of life of PVC is a real problematic case due to its high chlorine and diverse additives content. Other sources of the halogen-containing flame retardants based especially on bromine substances are widely used to meet the flammability standards of products. Several recent scientific works dealing with diverse aspects of plastics containing PVC and halogenated flame retardants are well summarized in Materials [17–22].

There are not many adequate solutions to e-waste treatment and the recycling of the contained metals. One may mention the "hot process" which resembles incineration and / or conventional pyro-metallurgical processes for the extraction of base metals (Cu, Pb ... ). The presence of commonly halogenated plastics complicates the operation at high temperature and causes the loss of some valuable elements. The "wet process", meanwhile, relies on multiple steps, apparatuses and the use of a wide range of inorganic and organic reagents which are not always environmentally friendly. The use of pyrometallurgical and hydrometallurgical processes for the recovery of high-value metals from wastes was reviewed by Ding et al. [10]. Regarding smelting, it was noted that it is beneficial for the concentration of precious metals. Avarmaa et al. [11] indicated that several precious metals (gold, silver, palladium and platinum), found in end-of-life electronics, are recovered in the melted copper using a smelting process. It should be noted that high-value elements (Au, Ag, Se, Te, platinum group metals, etc.) are concentrated in the anode slime of primary copper extraction from sulfide materials. One may conclude that the processing of electronic wastes in conventional copper pyrometallurgy resulted in the concentration of the valuable elements in by-products such as the anode slime of the copper electro-refinery.

Recent studies dealt with various treatments of copper anode slime (CAS) recovering targeted elements. Among various methods used, the treatment by H2SO4-O2 and thiourea was given by Amer [12]. Leaching processes of the CAS using H2SO4 and HNO3 as digestion agents were also applied [13,14]. A combined approach, thiosulfate leaching followed by an electrodeposition, was described by Xiao et al. [15]. Use of NaOH for selenium dissolution was also developed [16]. In Part I of this investigation, the thermal behavior of CAS under an oxidizing atmosphere was described. Of special emphasis during this treatment was the recuperation of pure selenium oxide (SeO2) by cooling the gaseous phase during the CAS treatment.

However, limited current works are available for the thermal treatment of CAS under a dry halogenated atmosphere. In this framework, the work presented here deals with the thermal behavior of CAS supplied by a European copper plant under air in presence of polyvinyl chloride (PVC). A systematic physico-chemical characterization of the treatment products obtained under different experimental conditions has been developed in order to understand the reaction paths and mechanisms of the process for achieving a selective separation of the elements contained in the CAS. A comparison of results obtained during the treatment of CAS in solely air atmosphere with those obtained in air + PVC is often exhibited to understand the intermediate steps involved during thermochemical treatment of the CAS. Furthermore, the preliminary thermal treatment of an e-waste sample containing brominated substances was also performed. This study was performed in the frame our research program focusing mostly on the treatment of low-grade raw materials and solid residues by a thermo-chemical

route [23–28] and on the valorization of certain iron bearing wastes via chemical synthesis of new and green materials [29–34].

#### **2. Materials and Methods**

A sample of CAS, with a median particles size lower than 63 μm, was used for this research work. Diverse analytical methods were used for the physico-chemical characterization of the CAS sample, but only the results of scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD) analyses are shown in this paper. The SEM-EDS and XRD equipment as well as the analytic protocol were described in Part I [1].

A sample of pure polyvinyl chloride (PVC) (without additives) was also used for this study. The e-waste sample was constituted of printed circuit boards (PCBs) obtained from end-of-life computers.

The PVC sample and the mixture of (CAS + PVC) sample with a mass ratio CAS/PVC = 1 were conditioned as pellets of approximately centimetric size (Figure 1) prior to thermal treatment. The PCBs were cut into strips sectioned at (10 × 2) cm without further treatment. Isothermal experimental tests for the treatment of CAS, PVC samples and mixtures of CAS with PVC (CAS + PVC) as well as for the e-waste sample were conducted in horizontal system including air metering and a static tubular furnace able to reach 1600 ◦C with a uniform temperature segment of at least 20 cm. The specimen holder (Figure 1) and the reactor were made of quartz material which is resistant towards the working conditions. To experiment with this process, a pre-weighted sample of several grams was introduced directly into the furnace preheated at a fixed temperature. When the dwell time is reached, the sample is removed from the furnace and cooled down to room temperature. Condensation of the outlet gases at room temperature led to the recovery of the vapor phase as condensates. Solid products (residues and condensates) were examined by SEM-EDS and XRD analysis.

**Figure 1.** Optical image of polyvinyl chloride (PVC) and (copper anode slime (CAS + PVC) pellets used for the thermal treatment.

#### **3. Results**

#### *3.1. Elemental and Mineralogical Analysis of Copper Anode Slime (CAS) and Polyvinyl Chloride (PVC) Samples*

As noted in Part I [1], several research reports [12–16,35–38] emphasized the complex nature of the CAS based on their elemental, mineralogical and morphological analysis. The particular morphology of the studied CAS sample is also exhibited by an SEM image as illustrated in Figure 2a, meanwhile the multi-elemental composition (Cu, Se, Ag, S, O, Au, Si, Te, Cl) is clear in the general EDS spectrum of the CAS (Figure 2b). The presence of carbon in the EDS spectrum is probably resulting from the carbonaceous matter in the CAS sample and the carbon coating used to make the sample conductive for the SEM-EDS analysis.

**Figure 2.** Scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS) results of initial copper anode slime: (**a**) general view (backscattered electron micrograph "BSE") of the used sample; (**b**) overall EDS analysis of the used sample.

A clearer view revealing the atypical morphology of the CAS sample is shown in Figure 3 and, as depicted previously [1], there are multiple particles that are irregularly and shell shaped. The SEM-EDS microanalysis data given in Table 1 indicates Cu, Se and Ag (spot n◦ 1, 4 and 5) are frequently associated. Sulfur and to some level tellurium are also found in the spots probed; finally, gold is identified frequently in the finest particles (spot n◦ 4 and 5). Several explanations for the particular state of CAS particles and their composition are provided in Part I [I] of this investigation and there are related mostly with the thermochemical reactions developing during smelting and refinery of copper.

**Figure 3.** SEM-BSE image of initial copper anode slime. Numbers 1 to 5 indicate the spots for microanalysis.

**Table 1.** Elemental composition of copper anode slime analyzed by SEM-EDS.

1 wt% and at% represent mass and atomic percentage, respectively.

The XRD diffractogram of CAS is drawn in Figure 4. It detects the presence of eucairite (CuAgSe), confirming the microanalysis performed by SEM-EDS. Furthermore, there are, in the diffractogram of CAS, some peaks corresponding to Cu2Se, Cu2S, CuSeS, as well as to non-stoichiometric compounds with an absence of certain peaks probably due to crystallite orientation and these phases are defined as copper selenide sulfide (Cu2−xSeyS1−y). The XRD peaks for the Au-bearing phase match mostly with fischesserite (Ag3AuSe2). This phase composition (with substitution of Ag by Cu) is also revealed by SEM-EDS analysis (spot n◦ 4 and 5 in Table 1). Finally, Quartz (SiO2) completes the list of crystallized phases identified by XRD in the CAS sample.

**Figure 4.** X-ray diffractogram (XRD) of copper anode sample; data adapted from [1].

The pure PVC sample is constituted of near-spherical particles shapes of size less than 100 μm (Figure 5a). As expected, chlorine and carbon are the only elements revealed (Figure 5b) within the element detection threshold of the SEM-EDS instrument. The XRD pattern of the used PVC sample, exhibited several diffuse halos indicating the amorphous nature of PVC.

**Figure 5.** SEM-EDS results of initial PVC: (**a**) general view (BSE micrograph) of the used sample; (**b**) overall EDS analysis of the used sample.

#### *3.2. Thermal Treatment of a Mixture of (CAS* + *PVC) and PVC Sample in Air for 1 h*

Several grams of the copper anode sample mixed with PVC (CAS + PVC, CAS/PVC = 1) and conditioned as pellets (Figure 1) were used for isothermal tests performed between 195 and 770 ◦C in air atmosphere with a flow rate of 25 L/h. The evolution of the % mass loss (%ML) as a function of the treatment temperature is plotted in Figure 6. The %ML curve shape presents a regular continuous mass loss rise for temperatures up to about 600 ◦C. The examination of Figure 6 with the data obtained for the treatment of CAS alone in air atmosphere (Figure 7) shows a big difference in the curve shape, at least at low temperature. The mass gain in Figure 7 was attributed to the oxidation of several CAS elements and synthesis of combined oxides [Cu4O(SeO3)3, Cu2O(SeO3)], thereafter, their decomposition and subsequent volatilization of SeO2 led to the mass loss observed at higher temperature [1].

**Figure 6.** Plot of the mass loss of the sample versus temperature during treatment of CAS + PVC in air for 1 h.

**Figure 7.** Plot of the mass loss of the sample versus temperature during treatment of CAS in air for 1 h.

One option to clarify these different behaviors was to check the reaction of PVC with air at various temperatures. Additives and composition information are identified by analyzing the reaction products of the thermal treatment of (CAS + PVC) in air atmosphere, as described in Section 3.3.

Figure 8 is a plot of %ML of the PVC sample versus temperature ranging from 165 to 505 ◦C. It is clear from this figure that there are two distinguishable steps describing the thermal treatment of PVC in air atmosphere. The first step (T < 300 ◦C) could be attributed to a complete removal of chlorine during the thermal degradation of PVC. The value of 56.62 % ML (corresponding to the theoretical chlorine content of PVC) at 275 ◦C seems to indicate that all chlorine is volatilized (as HCl) leaving behind a carboniferous residue (char). The removal of chlorine is also confirmed by SEM-EDS analysis of the residue obtained at 275 ◦C. Other confirmation of HCl generation was also the acidity (pH) monitoring of an alkaline solution scrubbing out-gases issued from PVC treatment between 225 and 275 ◦C. After a latent period, the solution pH decreased abruptly from 12.5 to 0.50 as the reaction progress at 250 ◦C. As shown by the Arrhenius diagram in the miniaturized graphic in Figure 8, the mean apparent activation energy (Ea) for the chlorine removal is calculated to be about 120 kJ/mol between 165 and 250 ◦C. The second step for the treatment of PVC in air was observed beyond 300 ◦C and may attributed to the reaction of the hydrocarbons with oxygen giving carbon oxides and water vapor as a final reaction product.

**Figure 8.** Thermal behavior of a pure PVC sample in air for 1 h.

#### *3.3. Analysis of the Reaction Products*

Residues produced from isothermal processing of CAS + PVC under air atmosphere were evaluated by XRD and SEM-EDS techniques and results were compared with those obtained during the treatment of only CAS in air atmosphere.

Figure 9 displays the XRD patterns of the residue of CAS+PVC treated at 195 ◦C. Besides the characteristic peaks of the initial CAS phases (CuAgSe, Ag3AuSe2, Cu2−xSeyS1−y and SiO2), there are new crystallized phases, namely cuprous chloride (CuCl), silver chloride (AgCl), and umangite (Cu3Se2). With this phase identification and based on thermodynamic calculations [39], one can deduce that the following overall reactions may have occurred:

$$\rm 1/4Cu\_2Se\_{(s)} + HCl\_{(g)} + 1/4O\_{2(g)} \to 1/2CuCl\_{(s)} + 1/4SeCl\_{2(g)} + 1/2H\_2O\_{(g)}\tag{1}$$

$$\rm{2Cu\_2Se\_{(s)} + HCl\_{(g)} + 1/4O\_{2(g)} \to Cu\_3Se\_{2(s)} + CuCl\_{(s)} + 1/2H\_2O\_{(g)}}\tag{2}$$

$$1/4\text{Ag}\_2\text{Se}\_{\text{(s)}} + \text{HCl}\_{\text{(g)}} + 1/4\text{O}\_{2\text{(g)}} \to 1/2\text{AgCl}\_{\text{(s)}} + 1/4\text{SeCl}\_{2\text{(g)}} + 1/2\text{H}\_2\text{O}\_{\text{(g)}}\tag{3}$$

The standard Gibbs energy changes (ΔrG◦) at 100 ◦C [39] for the reaction (1), (2) and (3) are −76.41, −116.19 and −68.84 kJ/mol HCl, respectively showing the thermodynamic reactivity of the targeted phases with respect to HCl in presence of oxygen. The selenium dichloride (SeCl2) is considered for the thermodynamic calculation among the selenium chlorides (Se2Cl2, SeCl2, SeCl4, SeOCl2), although it is difficult to give an exact reactional scheme of selenium chloride formation. However, the formation of CuCl (chlorine being in the PVC) instead of CuO and the volatilization of selenium chloride (s) explain the mass loss of sample (CAS + PVC) treated at low temperature (see Figure 6). The characteristic XRD peaks of Cu3Se2 is observed in the XRD patterns of (CAS + PVC) treated at 195 ◦C (Figure 9). The phase diagram of the system Cu-Se [40] indicates the presence of Cu3Se2 which melted incongruently over 112 ◦C. One may assume that the Cu3Se2 appeared (Equation (2)) as a stable phase, perhaps during the sample cooling.

**Figure 9.** XRD patterns of a CAS raw sample and (CAS + PVC) treatment product in air at 195 ◦C.

The presence of the partially chlorinated CuAgSe phase is observed by SEM-EDS examination for a residue obtained at 225 ◦C. The spot n◦ 2 of Figure 10 seems to indicate a small particle likely to be the CuAgSe phase. Its neighbor (spot n◦ 1) should be a mixture between the CuAgSe phase and Cu-Ag chlorides that are in solid state at this temperature.

**Figure 10.** SEM-EDS results of a residue issued from the (CAS+PVC) treatment at 225 ◦C in air atmosphere: (**a**) general view (BSE micrograph); (**b**) EDS analysis of spot n◦ 1 and 2.

The XRD results of the residues (CAS+PVC) obtained at temperatures higher than 320 ◦C show a good similarity with those obtained during the treatment of CAS in the absence of PVC. However, as shown in Figure 11, the decomposition of neo-formed combined oxides [e.g., Cu4O(SeO3)3] and the appearance of new phases [e.g., CuO], occurred apparently, at lower temperatures in the case of CAS treatment in presence of PVC. One of the plausible hypotheses is that the temperature in the reaction

zone can be significantly higher than the fixed furnace temperature due to the highly exothermic nature of the reactions of the PVC degradation under oxygen. Such exothermic phenomena were also observed previously during the treatment of only 2 g of sulfides with chlorine at 300 ◦C resulting in a temperature increase in the reaction zone of about 30 ◦C [41,42].

**Figure 11.** Comparison of XRD patterns of the product issued from the treatment of CAS and (CAS + PVC) samples in air at 415 ◦C.

A summary of the crystalline phases identified by XRD in the treatment residues obtained during the treatment of CAS and that of the mixture (CAS + PVC) in air for 1 h is given in Tables 2 and 3, respectively. As shown in Table 2, the phases of the residue obtained at 225 ◦C are those revealed in the CAS raw sample. Eucairite (CuAgSe) is still stable at 320 ◦C, while the characteristic peaks of Cu2-xSeyS1-y and Ag3AuSe2 phases disappeared at this temperature. The XRD of residue produced at 320 ◦C indicated the formation of new phases such as: [Cu4O(SeO3)3], [Cu2O(SeO3)]. Metallic silver is also identified in this treatment residue; note that the main XRD peaks of Ag◦ and Au◦ are overlapped. The panorama of the residues phases at 415 ◦C is identical of that of 320 ◦C, though the intensities proportion of phases changed suggesting the appearance of new phases.

**Table 2.** Summary of XRD results of the residues issued from the treatment of CAS in air for 1 h.

1 Initial Sample.

**Table 3.** Summary of XRD results of the residues issued from the treatment of the mixture (CAS + PVC) in air for 1 h at various temperatures.

At 505 ◦C [Cu2O(SeO3)] is still the main crystallized phase, but tenorite (CuO) is also identified and becomes the main phase at higher temperature. According to the data reported in Part I [1] and those given by Fokina et al. [43], the two steps of Cu4O(SeO3)3 conversion into CuO and SeO2 as final products can be described by Equations (4) and (5):

$$\text{Cu}\_4\text{O(SeO}\_3\text{)}\_3 \to 2\text{Cu}\_2\text{O(SeO}\_3\text{)} + \text{SeO}\_2 \tag{4}$$

$$2\text{Cu}\_2\text{O(SeO}\_3) \to 4\text{CuO} + 2\text{SeO}\_2 \tag{5}$$

Analysis of the XRD diffractograms for the residues obtained at 685 ◦C and 770 ◦C confirms the presence of well-crystallized phases of silver (Ag◦), tenorite (CuO) and quartz (SiO2), which was present in all analyzed residues.

The reaction of HCl released during the partial degradation of the PVC with CAS at 195 ◦C (Table 3) led to the synthesis of new crystallized phases such as: CuCl, Cu3Se2 and AgCl which are still identified in the treatment residue obtained at 225 ◦C because at this temperature the rate of de-chlorination of PVC is slow and continuously producing the necessary HCl for 1 h of the experimental test (see Figure 8). At 320 ◦C, the phases identified in the treatment residues of CAS in the absence (Table 2) or in the presence of PVC (Table 3) are similar. One may hypothesize that starting from this temperature treatment, the kinetic of chlorine production (as HCl) from PVC accelerates, hence the contact time between CAS constituents and HCl gas is quite short. Furthermore, the used PVC is in powder form, which means that the temperature is almost uniform across the particles leading undoubtedly to the simultaneous and instantaneous de-chlorination of the PVC.

As mentioned above, a neo-formed phase such as CuO produced from thermal decomposition [Cu2O(SeO3)] via Equation (5) occurred at apparent lower temperature (at 415 ◦C) attributed to the heat release from constituents' interaction in the sample mixture (CAS + PVC). Besides, the characteristic peaks of Cu2O (d = 2.46 Å and d = 2.13 Å) appeared also in the XRD patterns of residues obtained at 415 ◦C and 505 ◦C exhibiting the effect of the carbon on the oxidation state of copper. These diffraction peaks are of low intensity for a temperature higher than 550 ◦C.

The XRD diffraction patterns of products for both CAS treatments are similar for the temperature higher than 505 ◦C (Tables 2 and 3). The XRD patterns of a CAS raw sample and its reaction product issued from the thermal treatment of CAS + PVC at 770 ◦C are compared in Figure 12. With a complex phase composition of a raw CAS sample (CuAgSe, Cu2−xSeyS1−y, Ag3AuSe2 and SiO2), the treatment residue at 770 ◦C is free of the selenium-bearing phase and it is composed of CuO, SiO2 and Ag◦ (and Au◦).

**Figure 12.** XRD diffractograms of a CAS raw sample and (CAS + PVC) thermal treatment product in air at 770 ◦C.

The EDS analysis of spot n◦ 1 (Figure 13) showed that Ag◦ (84.4 wt%) was the major constituent with some Au◦ (13.4 wt%) and Cu◦ (2.2 wt%). All smoothed particles had similar composition. The area noted by spot n◦ 2 was essentially composed of copper and oxygen with oxygen deficit to be CuO. The small area noted as n◦ 3 seemed to be composed of copper, silver and tellurium oxide (TeO2).

**Figure 13.** SEM aspects (BSE image) of the (CAS + PVC) sample treated at 770 ◦C in air atmosphere. Numbers 1 to 3 indicate the spots for microanalysis.

Likewise, the thermal treatment residues were examined by SEM-EDS. Figure 13 illustrates a typical morphology with a strong contrast indicating areas of distinct compositions. Data of SEM-EDX analysis of spots n◦ 1, 2 and 3 are reported in Table 4. The presence of well smoothed particles (image in Figure 13) indicates that the smelting of the metallic phase had been occurring during the treatment. Although the melting points of pure metals (Cu, Ag, Au) are higher than the temperature of the experimental tests, according to phase stability diagrams [40], the liquid phase appeared at temperatures lower than those of the fusion point of these metals. Furthermore, the heat release from the exothermic reactions can increase the sample temperature leading to local fusion of the treatment residue.

**Table 4.** Elemental composition (EDS data) of the (CAS + PVC) treated at 770◦C in air atmosphere.

1 wt% and at% represents mass and atomic percentage, respectively.

The chosen copper anode slime sample contained a significant amount of selenium and tellurium, which belong to the scattered elements category [44]. As reported previously [45–47], these elements are used in thin films (CIGS—copper indium gallium selenide, and CdTe—cadmium telluride) and used in second-generation modules of photovoltaic panels. Recovery of these elements from by-products, end-of-life solar photovoltaics and other wasted materials will be a challenge of future research works to meet the volume of industrial demand.

These results encompassed some characteristics for the thermal treatment of a copper by-product in the presence of PVC and allowed us to understand the behavior of selected element compounds during the process. However, end-of-life materials (especially electric and electronic devices) are generally more complex in elemental, chemical and mineralogical composition of inorganics, with the presence of various organic matters and additives incorporated for enhancing the functional and commodity properties of the designed appliances.

The following section gives an idea about the interaction of bromine-bearing substances with valuable metals of an e-waste (printed circuit boards—PCBs).

#### *3.4. Preliminary Results for Treatment of E-Waste in Air*

Several selected research works [10,11,48–52] were devoted to the recovery of high value added metals and other components from e-waste by using various methods. A weak point for the metal recycling from e-waste is the high amounts of halogenated substances disturbing the thermal extraction process. Of particular interest are the data reported by Hino et al. [48] and Szałatkiewicz [51] with respect to the elemental and material compositions of the PCBs originating from discarded computers. The organic epoxy resin, inorganic glass fiber and metal elements represented 31.8 wt%, 37.6 wt% and 30.1 wt% of the PCBs, respectively. The bromine content in the organic substances was 5.07 wt%.

In the previous sections, it has been demonstrated that hydrogen chloride issued from PVC decomposition can react with several metal compounds generating their respective chlorides. Chlorine and bromine substances are often embedded in the plastic as flame retardants and they are still widely used despite environmental concerns. To gain an insight into the thermal behavior of the e-waste (PCBs of the obsolete end-of-life computers), isothermal tests under an air atmosphere were performed at 500 ◦C for reaction times of 0.25, 0.50, 0.75, 1.0 and 2.0 h. As the physical sample is composed of plate strips cut at about (10 × 2) cm, it was useful to repeat the experimental tests (3 times) at a given reaction time in order to have a reliable correlation between % ML of sample and the reaction time. This allowed us to overcome the impact of macroscopic heterogeneity with respect, at least, to plastic content. Additionally, for the reaction time of 1 h, 10 experimental tests of PBCs

treatment in air atmosphere were performed to carefully check the reproducibility of experimental tests and to attain a better sampling of the obtained products. All the results are displayed in Figure 14.

**Figure 14.** Mass change of the sample versus time for the treatment of printed circuit boards (PCBs) at 500 ◦C: (**a**) % mass loss (%ML) versus time; (**b**) %ML obtained for each test number at reaction time of 1 h.

About 24.5% ML were obtained during the treatment of PCBs sample for 0.25 h in air atmosphere (Figure 14a). The % ML of the sample increased slightly with reaction time to reach 29.0% during the treatment at 2.0 h. The experimental tests for 1 h gave mass losses oscillating between 25.5% and 29.0% with a mean value of 27.2% (Figure 14b). The small influence the treatment time had on the sample loss is probably due to the high reactivity of the organic matter towards air (O2), therefore likely leading to a temperature increase in the reaction zone. The organic matter content (31.8%) of the PCBs from discarded computers previously reported [48,51] seems to be in good agreement with the results shown in Figure 14. The bromine content of the PCBs organic substances reported to be around 5 wt% in references [48,51] is assumed to apply to the similar e-waste used in the present study.

The treatment residue obtained for 1 h of treatment was sieved and the fine fraction (less than 210 μm) was analyzed by SEM-EDS technique. Likewise, the solid condensate was examined by the same technique.

A general SEM image of the treatment product is displayed in Figure 15a. Although most metals (especially Cu) are found in the coarse fraction of centimetric size, this fine fraction of the treatment product still contains Sn, Cu and Pb compounds (spectrum in Figure 15b). Si, Ca, Al and Mg are often found in the sticks (see SEM image of Figure 15a) being used as reinforced fibbers and/or glass weaves for the plastics.

Punctual analyses by EDS of various areas of SEM image of Figure 16 give different compositions as reported in Table 5. There are areas rich in lead (spot n◦ 1) and in tin (spot n◦ 2). Tantalum (spot n◦ 3) is almost certainly derived from tantalum capacitors. The EDS analyses of spot n◦ 4 represents mostly the elemental composition of an inorganic filler particle.

**Figure 15.** SEM-EDS results of a residue obtained from the treatment of the e-waste sample at 500 ◦C in air atmosphere: (**a**) general view (BSE micrograph) of the residue; (**b**) overall EDS analysis of the residue.

**Figure 16.** SEM aspects (BSE image) of a residue area obtained from the treatment of the e-waste sample at 500 ◦C in air atmosphere for 1 h. Numbers 1 to 4 indicate the spots for microanalysis.

**Table 5.** Elemental composition (EDS data) of the areas displayed in Figure 16.

1 wt% and at% represent mass and atomic percentage, respectively.

The attractive result of the SEM-EDS analysis is given in Figure 17 and Table 6. Besides metals (Ag, Cu, Pb, Sn ... ), at various proportions, there is an appreciable amount of bromine (spots n◦ 1 to 3) indicating that bromine is bonded with part of the metals as bromides.

**Figure 17.** SEM aspects (BSE image) of a residue area obtained from the treatment of the e-waste sample at 500 ◦C in air atmosphere for 1 h. Numbers 1 to 3 indicate the spots for microanalysis.

**Table 6.** Elemental composition (EDS data) of the areas displayed in Figure 17.

1 wt% and at% represents mass and atomic percentage, respectively.

As shown in Figure 18, gold, which is used in PCBs to assure circuit board contacts, seems to be inert to the treatment at this temperature.

**Figure 18.** SEM-EDS results of a residue obtained from the treatment of the e-waste sample at 500 ◦C in air atmosphere: (**a**) general view (BSE micrograph) of a residue area; (**b**) punctual EDS spectrum.

A thermodynamic calculation [39] showed that the values of the ΔrG◦ for the reaction (6), (7), (8) and (9) at 500 ◦C are −119.80, −124.11, −143.22 and –119.97 kJ/mol HBr, respectively. Such negative values suggest that the envisaged reactions are favorable from the thermodynamic point of view. The species AgBr, CuBr, PbBr2 and SnBr4 are chosen for their predominant thermodynamic stability in the studied system (Metal-O-Br) and based on the thermochemical data availability.

$$\rm Ag\_{(s)} + HBr\_{(g)} + 1/4O\_{2(g)} \to AgBr\_{(l)} + 1/2H\_2O\_{(g)}\tag{6}$$

$$\rm Cu\_{(s)} + HBr\_{(g)} + 1/4O\_{2(g)} \to CuBr\_{(l)} + 1/2H\_2O\_{(g)}\tag{7}$$

$$1/2\text{Pb}\_{\text{(s)}} + \text{HBr}\_{\text{(g)}} + 1/4\text{O}\_{2\text{(g)}} \to 1/2\text{PbBr}\_{\text{2(l)}} + 1/2\text{H}\_2\text{O}\_{\text{(g)}}\tag{8}$$

$$1/4\text{Sn}\_{\text{(s)}} + \text{HBr}\_{\text{(g)}} + 1/4\text{O}\_{2\text{(g)}} \to 1/4\text{SnBr}\_{\text{4(g)}} + 1/2\text{H}\_2\text{O}\_{\text{(g)}}\tag{9}$$

As indicated in Section 2, the exit gases were cooled resulting in the condensation of the vapor phase and the recovery of a solid condensate mixed often with unburnt carbonaceous matter, soot and liquid giving the visual appearance of a pasty mass. SEM-EDS results of a condensate are shown in Figure 19 with an EDS analysis of spot n◦ 1 corresponding roughly to PbBr2. As the vapor pressure of PbBr2 is near to 0.1 kPa [39], its presence in the condensate is probably due to it being brought back by the carrier gas and/or thanks to temperature increase enhancing its volatilization. Another EDS punctual analysis displayed in Figure 20b, noted as spot n◦ 2 of SEM image, suggested most likely the stannic bromide (SnBr4) generated from the condensation of gaseous tin bromide [SnBr4(g)] in the cooled part of the reactor. The obtained results showed that several metals could be concentrated in the vapor phase via volatilization of the neo-formed halides during the thermal process.

**Figure 19.** SEM-EDS results of a condensate issued from the e-waste sample treated at 500 ◦C in air atmosphere: (**a**) general view (BSE micrograph); (**b**) EDS analysis of spot n◦ 1.

**Figure 20.** SEM-EDS results of a condensate issued from the e-waste sample treated at 500 ◦C in air atmosphere: (**a**) general view (BSE micrograph); (**b**) EDS analysis of spot n◦ 2.

As revealed during this study, the extraction of the critical and high-value elements from the chosen by-product and end-of-life materials represents a challenge due to the chemical and mineralogical complexity of their components as well as to the selectivity of the extractive chemistry of different metals for an efficient separation. Moreover, fair thermodynamic data, the ability to gather phases differentiation, punctual information about elemental content, in addition to monitoring the morphological and textural evolution of the thermally treated samples, are all contributing to a better understanding of the reaction mechanism involved and processing steps for the studied cases. Other aspects of this investigation, dealing with mass balance of the processes and assessment of technical and economical evaluation, should be carried out in future studies.

#### **4. Conclusions**

Copper Anode Slime (CAS) is a complex material containing the targeted elements (Ag, Au, Se, Te, Cu ... ) distributed in diverse mineralogical phases such as Ag3AuSe2, CuAgSe, Cu2−xSeyS1−y.

The interaction of CAS constituents with HCl, issued from the degradation of polyvinyl chloride (PVC) under in an air atmosphere, started from about 200 ◦C leading to the favorable formation of AgCl and CuCl. Selenium is probably volatilized as selenium chlorides, most likely as SeCl2(g).

The isothermal degradation of PVC in an air atmosphere is a two-step process. The PVC de-chlorination occurs at temperature lower than 300 ◦C and proceeds with an apparent activation energy of around 120 kJ/mol. The second step should be attributed to the reaction of oxygen with carbonaceous matter generated in the first step. Full sample degradation and volatilization of the reaction products were achieved during treatment of PVC at about 500 ◦C for 1 h.

The reaction of HCl generated from PVC with CAS at temperature higher than 275 ◦C remained limited because the generation rate of HCl was higher than that of the interaction of HCl with CAS constituents.

The thermal treatment of CAS + PVC beyond 300 ◦C gave roughly similar results to the processing of CAS alone in air atmosphere. The formation of combined copper-selenium oxides, followed by their decomposition allowing solid copper oxides are the main steps of this treatment.

The final residue of the CAS + PVC treatment in air at temperature higher than 600 ◦C is composed of CuO (Cu2O) and alloys of Ag-Au (with some Cu◦), while tellurium is found as oxide (TeO2), and silica (SiO2) which is unreactive with respect to the thermal treatment. Further treatment of this product is required for the final separation of these high-value element compounds.

The bromine-bearing flame retardants of the printed circuits boards (PCBs) also appeared to be a good halogenating agent for several components of this e-waste. Bromides of copper, lead and tin, synthetized through the reaction of the evolved HBr with their respective metals, are distributed between residue and condensate of the PCBs treatment at 500 ◦C under air atmosphere. Further studies linked with various experimental parameters should be undertaken for a selective separation of the synthetized halides.

**Author Contributions:** Conceptualization, N.K., E.A., F.P. and J.Y; Formal analysis, S.S., S.D. and F.D.; Investigation, N.K., S.D. and F.D.; Visualization, S.S. and F.D.; Resources, N.K., F.P. and J.Y.; Writing—original draft, N.K., E.A., S.S. and F.P.; Writing—review and editing, N.K., E.A., F.P. and J.Y. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was carried out within the framework of French projects namely: *(i)*—PEPS-Urban mine-2014 (CNRS-INSIS); *(ii)*—"Investissements d'avenir"—ANR-10-LABX-21-01/LABEX RESSOURCES21; *(iii)*—ANR CARNOT programme.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

*Article*


**Land-Atmosphere Interaction in the Southwestern Karst Region of China Land-Atmosphere Interaction in the Southwestern Karst Region of China**

Jiangbo Gao, Wenjuan Hou, Kewei Jiao and Shaohong Wu Jiangbo Gao, Wenjuan Hou, Kewei Jiao and Shaohong Wu

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/64740

#### **Abstract**

Land-atmosphere interaction in the southwestern Karst region of China was investigated from two aspects: response of land cover to climate change and climatic effects of Karst rocky desertification. The first part focused on the temporal-spatial variation of growing-season normalized difference vegetation index (NDVI) and its relationship with climate variables. The relationships between growing-season NDVI with temperature and precipitation were both positive, indicating its limiting role on the distribution and dynamic of vegetation cover in the study area. The second part was designed to investigate whether the changed vegetation cover and land surface processes in the Karst regions was capable of modifying the summer climate simulation over East Asia. It was shown that land desertification resulted in the reduced net radiation and evaporation in the degraded areas. The East Asian summer monsoon was weakened after land degradation. Such circulation differences favored the increase in moisture flux and clouds, and thereby causing more precipitation in southeast coastal areas. Based on the above findings, it can be concluded that vegetation cover in Karst region was sensitive to climate change at larger scale, and on the other hand, there was significant feedback of vegetation cover change to regional climate by altering water and energy balance.

 Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


**2. Single-gene pharmacokinetics disorders**

#### **2.1 Pseudocholinesterase deficiency**

Pseudocholinesterase is a plasma enzyme produced in the liver that is responsible for the metabolism of common muscle relaxants, including succinylcholine and mivacurium [25]. The inherited form of the enzyme transfers in an autosomal recessive manner. Patients with defective inherited forms of pseudocholinesterase (heterozygotes and homozygotes) present with prolonged muscular paralysis. Acquired pseudocholinesterase deficiency can develop in a variety of diseases or as a side effect of certain medications [26]. Pseudocholinesterase deficiency can be induced by malnutrition, pregnancy and the postpartum period, burns, liver illness, renal disease, cancer, infections, and medications such as steroids and cytotoxic agents [27]. Both acquired and hereditary defects are considered uncommon. Caucasian males of European origin, as well as Alaskan Native tribes, have the highest frequency of pseudocholinesterase deficiency [28]. In pseudocholinesterase-deficient patients, there is no particular therapy for neuromuscular paralysis; nevertheless, respiratory assistance with mechanical ventilation can be provided until the neuromuscular blockade is resolved [29]. Nondepolarizing neuromuscular blockers, such as atracurium, rocuronium, and vecuronium, are indicated for those with pseudocholinesterase deficiency. In addition, relatives of those who have been diagnosed with pseudocholinesterase deficiency are advised to get tested for the condition [30].

#### **2.2 Acute intermittent porphyria**

Acute intermittent porphyria (AIP) is a pharmacogenetic disease caused by a porphyrin metabolic defect characterized by a lack of porphobilinogen deaminase and a rise in the activity of delta-aminolevulinic acid synthase—two essential enzymes required for heme production [31]. Patients may have stomach discomfort, vomiting, muscular weakness, constipation, and neuropsychiatric symptoms during an episode. Clinical episodes are produced by many drugs (including barbiturates, antiseizure drugs, and sulfonamide antibiotics), hormones, and dietary variables, all of which induce hepatic delta-aminolevulinic acid synthase [32].

The most accurate approach for confirming AIP in patients and their symptom-free relatives is DNA analysis. The hydroxymethylbilane synthase (HMBS) gene is directly sequenced to discover a mutation in the proband as well as asymptomatic gene carriers among family members [33]. The sensitivity of the mutation analysis ranges from 90–100%. So far, 391 mutations in the HMBS gene have been reported. Thus, DNA testing in a family's index case may be more difficult and time-consuming, but mutation analysis thereafter may quickly identify numerous family members at risk [34].

Heme infusions are frequently used to reduce the intensity and frequency of recurring episodes. The goal of this treatment is to significantly lower the level of porphyrin precursors in the blood. Most individuals react effectively, although longterm therapy may lead to exogenic heme dependency. As a result, a patient's heme need may grow from monthly to twice-weekly infusions, making treatment discontinuation difficult due to significant porphyric symptoms. The use of heme preparations on a regular basis might cause thrombotic problems in the superficial veins, necessitating the use of a permanent central venous catheter [35]. Furthermore, long-term heme therapy might result in iron excess and hemosiderosis, which can cause organ damage. Hepatopathy, heart failure and endocrinopathies may arise as a result of the disease progressing. Iron burden in organs is shown by computed tomography (CT) or magnetic resonance imaging (MRI) [36]. Venesections are generally unpopular, although iron chelates can help. Preventative actions can be taken if family members are tested to determine whether they are genetic carriers. Symptomatic treatment, a high carbohydrate diet, and intravenous hematin injection are all used to treat attacks [37].

#### **2.3 Drug acetylation deficiency**

N-acetyl transferase (NATS) activities in human hepatic drug metabolizing enzymes have previously been identified as a source of inter-individual heterogeneity in drug metabolism [38]. The liver's cytochrome P450 enzymes are primarily responsible for phase I oxidation, whereas phase 2 conjugations include glucuronidation, sulfation, and acetylation [39]. Two genes (NAT 1) and (NAT 2) are now known to control N-acetyl transferase (NAT), with NAT 2 A and B accounting for clinically significant metabolic variance [40].

Caffeine, isoniazid, nitrazepam, and sulfonamides are among the many common medications that are acetylated. Aromatic and heterocyclic amines are also carcinogenic, which has led to the theory that NAT genotypes are linked to cancer risk. Individuals can be divided into two groups after receiving sulfamethazine, caffeine, or another marker drug and having plasma and urine drug concentrations measured after a standard time interval: fast acetylators with only low concentrations of the parent drug remaining in the blood and slow acetylators with much higher concentrations of the parent drug remaining in the blood [41]. The frequency of fast and slow

*Interplay between Pharmacokinetics and Pharmacogenomics DOI: http://dx.doi.org/10.5772/intechopen.108407*

acetylators varies by ethnicity; Caucasian and Negro populations have almost equal numbers of fast and slow acetylators, whereas Oriental races have over 90% quick acetylators. The slow acetylator phenotype predominates among Arab people in Asia (e.g., Saudi Arabia and the United Arab Emirate) [42, 43] and North Africa (e.g., Egypt and Morocco) [40, 44].

### **3. Genetic variants affecting pharmacokinetics**

Genetic variation in drug-metabolizing enzymes and/or drug transporter genes might impact drug exposure in terms of PK key parameters, such as maximum drug concentration (Cmax) and area under the curve (AUC) [45]. These differences can affect a patient's loading dose, maintenance dose, dosing interval, and as a result, medication response and safety [46, 47].

#### **3.1 Pharmacogenomics of drug-metabolizing enzymes**

In the last decade, technical advancements in gene scanning and gene variant identification have substantially increased our understanding of the function of pharmacogenetics in drug metabolism [48, 49]. The number of genetic variants identified for genes coding for drug-metabolizing enzymes (DMEs) considerably increased in the early 2000s and continues to increase. Variation in drug metabolism and drug response can be caused by temporary factors, such as transient enzyme inhibition and induction, or by permanent causes, such as genetic mutation, gene deletion, or amplification among people of the same body weight and on the same medicine dosage. However, not all variants result in significant changes in enzyme activity. Genetic polymorphism can be associated with three phenotype classes based on drug metabolizing ability: the extensive drug metabolizer phenotype (EM) is found in the general population; the poor drug metabolizer phenotype (PM) is caused by mutation and/or deletion of both alleles and is linked to the accumulation of specific drug substrates; and gene amplification causes the UM phenotype, which results in increased drug metabolism [50]. The cytochrome P450 enzymes in families 1–3 mediate 70–90% of all phase I-dependent metabolism of available drugs [51]. The polymorphic forms of P450s are responsible for the development of approximately 86% of the reported adverse drug reactions (ADRs) of substrate drugs. Polymorphic enzymes (in particular, CYP2C9, CYP2C19, and CYP2D6) mediate around 40% of P450-mediated drug metabolism [52]. The major CYP450 forms that are important in human drug metabolism are shown in **Table 1**, together with their main substrates and the clinical consequences of the polymorphism.

#### **3.2 Pharmacogenomics of drug transporters**

The distribution of drug transporters in tissues key to pharmacokinetics, such as the intestine (absorption), blood-brain barrier (distribution), liver (metabolism), and kidneys (excretion), strongly suggests that genetic variation associated with changes in protein expression or function of these transporters may have a substantial impact on systemic drug exposure and toxicity [53]. In the last decade, a greater focus has been given to the impact of genetic variation in membrane transporters on the pharmacokinetics and toxicity of numerous therapeutic drugs [54]. While most transporter-related pharmacogenetic research has been related to classic genes

#### **Table 1.**

*CYP450 enzymes and related polymorphisms.*

#### **Table 2.**

*Drug transporters and related polymorphisms.*

encoding the outward-directed ATP-binding cassette (ABC) transporters, such as ABCB1 (P-glycoprotein), ABCC2 (MRP2), and ABCG2 (BCRP), more studies have been conducted in recent years evaluating genes encoding solute carriers (SLC) that mediate the cellular uptake of drugs, such as SLCO1B1 (OATP1B1) and SLC22A1 (OCT1) [55]. The main drug transporters are shown in **Table 2**, together with their main substrates and the clinical consequences of the polymorphism(s).


**Is Complete Re-Osseointegration of an Infected Dental Implant Possible? Histologic Results of a Dog Study: A Short Communication**

**Markus Schlee 1,2, Loubna Naili 3, Florian Rathe 1,4, Urs Brodbeck 5 and Holger Zipprich 6,\***

Received: 6 November 2019; Accepted: 9 January 2020; Published: 16 January 2020

**Abstract:** Complete reosseointegration after treatment of periimplantitis was never published yet. This short scientific communication reports about results of a randomized controlled preclinical study. An electrolytic approach was compared to a classical modality (ablative, cotton pellets soaked with sodium chloride solution and H2O2. For electrolytic cleaning a complete reosseointegration was achieved in several cases serving as a proof of concept.

**Keywords:** periimplantitis; electrolytic cleaning; augmentation; air flow; re-osseointegration; dog study


**7. Conclusion and future direction**

This chapter outlines some indicators related to the higher educational systems in the MENA region, such as the support given by instructional technologies to academics working in this region. The research instrument consisted of a series of questions for collecting data from the respondents by using three techniques: questionnaires, online meetings, and interviews.

Overall, the major goals of this chapter are:

A community of practice can be task and goal oriented to satisfy the need for cooperative achievements of goals and provide support for online learning [47].

This research provides a feasible idea for more achievements in higher educational sectors in the MENA region by including instructional technologies that facilitate the students' skills acquisition and assist higher educational systems.

It is also hoped that by setting the online labs indicator, this chapter may be useful to guide the development of higher educational systems in other regions. Similarly, it may find other indicators or activities related to learning that can develop and assist the higher educational systems in the MENA region and increase collaborative and cooperative work among their researchers.

Hopefully, for the middle/long term, involving other universities, in Iraq and other MENA countries in general, to become a part of this online labs community, either using the VISIR system or through the REXNet project, for sharing resources and knowledge among them and increasing collaborative and cooperative work among their researchers.


*2.4. Phylogeny and Clustering Based on Polarity*

In the D1 domain, it was observed that the polarity of thirteen amino acids among nineteen (24–42 aa) amino acids were found to be conserved across eighteen species. Based on the amino acids' polarity and non-polarity nature, the species were arranged in a phylogenetic tree (Figure 11).

It was found that *Homo sapiens, Pan troglodyte, Macaca mulatta*, and *Danio rerio* closer according to this analysis. *Pteropus alecto, Pteropus vampyrus*, and *Sus scrofa* occurred in parallel along with the above three and formed a different clade indicating the closeness based on polarity. Again, the case for *Gallus gallus, Rhinolophus ferrumequinum, Mustela putorius furo, Equus caballus*, and *Felis catus* is similar. Two separate groups, *Mesocricetus auratus, Manis javanica*, and *Capra hircus, Bos taurus*, were similarly placed nearby, indicating that the polarity of amino acids of the proteins for these species was similar. *Pelodiscus sinensis* and *Rattus norvegicus* occurred separately and were not grouped with any other species but bears similarity with both the groups containing species *Mesocricetus auratus, Manis javanica, Pteropus alecto, Pteropus vampyrus, and Sus scrofa*.

In the D2 domain, out of six amino acid long sequences, the polarity of three amino acids was conserved across eighteen species, and among them, one amino acid was a binding residue. *Homo sapiens, Pan troglodytes, Macaca mulatta, Pteropus vampyrus*, and *Pteropus alecto* were grouped together since the overall polarity of their amino acid chain was found to be similar, and, simultaneously, *Danio rerio, Mustela putorius furo, Gallus gallus*, and *Pelodiscus sinensis* were placed together. In addition, three groups comprising *Manis javanica, Capra hircus*, *Bos taurus, Sus scrofa*, *Rattus norvegicus, and Rhinolophus ferrumequinum*, respectively, were placed in close proximity based on their polarity and non-polarity of the amino acids in the protein sequence. However, *Equus caballus, Felis cattus*, and *Mesocricetus auratus* were placed separately since they did not show much resemblance based on polarity.

In the D3 domain of ACE2 sequences of *Salmo salar* and *Danio rerio*, there was an insertion of a polar amino acid into one of the binding residue positions that may affect the binding of ACE2 to that of RBD of SARS-CoV2 negatively. A total of three binding residues were already reported in the D3 domain, of which one of them remained conserved concerning polarity across the nineteen species. *Rattus norvegicus, Mustela putorius furo, Mesocricetus auratus*, and *Felis catus* were grouped under a single clade based on the polarity of their protein sequence. It was a similar case for *Danio rerio, Pelodiscus sinensis, Salmo salar*, and *Gallus gallus*. Due to the sequence similarity between *Pteropus vampyrus* and *Pteropus alecto*, their polarity of the protein sequence was also similar and thus grouped. Sequence similarity was also observed for *Homo sapiens, Pan troglodytes*, and *Macaca mulatta*, so again these were categorized together. Two groups comprised of *Rhinolophus ferrumequinum*, *Capra hircus*, and *Bos taurus, Sus scrofa*, respectively, were sorted together indicating their similar nature

of polarity and non-polarity of protein sequence. Lastly, *Manis javanica* and *Equus caballus* were placed separately signifying that the sequences of both species were quite distinct.

The individual groups of species based on the polarity of individual D1, D2, and D3 domains have emerged into six disjoint clusters (Figure 12).

Here, the clusters {*S*1, *S*2, *S*3}, {*S*16, *S*17, *S*18}, {*S*8, *S*14}, {*S*6, *S*13}, and {*S*10, *S*12} remained invariant with regard to the homology of full length ACE2 as well as polarity sequence of the D1, D2, and D3 domains.

**Figure 11.** Polarity sequence of the D1, D2, and D3 domains across all species alignment and associated phylogenetic relationships.

**Figure 12.** Clusters based on groups of species based on domain-wise polarity.