Control of acid mine draingage by passivation of reactive acid-generating materials.

摘要

Acid mine drainage (AMD) has been acclaimed as one of the most serious environmental issues facing the mining industry. The effects of mine drainage can limit recreational, industrial, and municipal use of downstream rivers. High remediation costs and the persistence of acid generation make acid drainage a major environmental and economical burden.; A new passivation process to treat acid drainage-producing pyritic wastes was investigated. Both pure pyrite and sulfide-containing rocks/tailings were used as samples in the study. Passivity is achieved with permanganate when a stable inert layer composed of manganese oxide is formed on the surface of pyritic materials. In this process solution pH is critical for the formation of the passive layer. The optimal solution pH is around 12.0. Dosage of magnesium oxide is also important for the stability of the passive layer.; Preliminary tests were conducted to evaluate the effectiveness of the passivation process on samples of different origins and to find the appropriate chemical dosages. Results of the preliminary tests were satisfactory for both pyrite sample and tailing samples. After preliminary tests, column tests were also conducted. The acid-producing potential of the processed sample was determined by using the hydrogen peroxide test and the humidity cell test. The results showed that under high solution pH and appropriate chemical dosage, pyritic materials can be successfully passivated.; Morphological study was performed on untreated and passivated pyrite samples using SEM and AFM methods. The results indicated the formation of an unreactive surface layer. This layer was stable in the leaching tests until the solution pH dropped to 2.0.; The study demonstrated that passivation with permanganate is an effective technique to control AMD producing rocks or tailings. It has the advantages of rapid kinetics, stable encapsulating layer, and no need for mining wastes removal.; In order to reduce the chemical cost of the passivation process modifications have been made so that potassium permanganate can be replaced by other inexpensive coating agent. In addition, the modified process is also made applicable in the relatively lower pH range (10.0) as opposed to pH (12.0) and is easy to deploy in the field.