acidity in water leaching from a mass of sulphide tailings is prevented by de - oxygenating the water prior to entering the mass . a cover comprising an electrolytic cell , either galvanic or impressed - current , gives rise to a cathode reaction in which the redox voltage of the water drops to 003 volts or less . the cover can be thinner , and much less expensive , than an equally - effective non - reactive cover . the electrolyte is water contained in water - retaining soil , or a depth of water , lying over the cathode . the cathode is steel mesh , or a layer of graphite , spread over the whole mass of tailings .