DES have also been studied for their potential use as more environmentally sustainable solvents for extracting gold and other precious metals from ore. Some solvent extraction work has been done using DES solvents, Mark Foreman at Chalmers has in recent years published several papers on this topic. He wrote about the use of the solvents for battery recycling from an applied point of view and he also published what may be the first ever serious study of solvent extraction of metals from DES. Foreman has also published two pure research papers on the activity issues in DES, in the first he pointed out that activity coefficients in DES do appear to deviate wildly away from their values in sodium chloride solution while in his later paper he provides a mathematical model for the activity coefficients in DES using the SIT equation.