Acid production from sulfide minerals using hydrogen peroxide weathering

Sulfide mineral weathering is a major source of acid generation in mining environments. Oxidation and hydrolysis reactions in soil and geologic material under earth surface conditions causes weathering of reduced sulfide minerals resulting in liberation of weathering products including acid. Pyrite and marcasite are minerals common in mine environments that cause acid generation. Many other sulfide minerals are present in mining environments which may or may not form acid upon weathering. Characterization of complex mineral assemblages containing S compounds is therefore critically important to pre-mine planning and postmine waste characterization. Despite the importance of mineral weathering behavior, little is known about the acid generation characteristics of common sulfide and sulfate minerals. To assess the response of common sulfide and sulfate minerals to oxidizing conditions, 13 minerals were subjected to treatment with 10% H₂O₂. The resulting leachate was analyzed for pH, electrical conductivity, S and titratable acidity. The sulfide minerals arsenopyrite, pyrite, chalcopyrite, pyrrhotite, marcasite and sphalerite demonstrated significantly elevated levels of titratable acidity and are acid generating in contrast to galena, chalcocite and all the sulfates. The sulfate minerals barite, anhydrite, gypsum, anglesite and jarosite were included in experimentation and were found not to form acid under strongly oxidizing conditions. Remediation strategies for disturbed lands containing reduced S minerals must therefore consider not only the total quantity of sulfide minerals present, but the specific mineralogy of the S compounds.