Author(s)

L J J Catalan & K L Wetteskind

Abstract

The processing of zinc concentrates in zinc refining plants generates large quantities of natrojarosite waste contaminated with heavy metals. Environmental regulations increasingly require treatment of this industrial waste. Stabilization/solidification (s/s) technology can be used to immobilize the heavy metals prior to long-term storage of the solidified waste as a heap in the field. Because the solidified material is porous and somewhat permeable, infiltration of rain and/or snowmelt water occurs at a slow rate, thus producing a leachate. The continued immobilization of heavy metals in the treated waste is dependent on the leachate remaining alkaline, since leachate pH is the major factor controlling the leaching of heavy metals. The leachate pH is in turn influenced by the progressive depletion of the alkalinity in the treated waste. An alkalinity depletion model has been developed to predict the evolution of leachate pH versus time for various infiltration situations. The model parameters are the effective alkalinity initially contained in the treated waste, the alkalinity depletion rate, the infiltration rate, and the height of the heap. Flow-through leaching tests have carried out using monolithic samples of treated natrojarosite waste in modified triaxial cells to determine experimental values for the effective alkalinity and the alkalinity depletion rate. Synthetic acid rain and a buffered solution of acetic acidsodium acetate were used as leachants. The model predicts that for a typical full-scale disposal situation, the leachate will remain alkaline and the heavy metals will stay immobilized in the treated waste for many thousands of years. 1 Introduction Natrojarosite waste is produced during the refining of zinc concentrates. Although pure natrojarosite has the formula NaFe3(SO4)2(OH)6, this waste also

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