Comparative column elution of jarosite waste and its autoclaved product - Evidence for the immobilization of deleterious elements in jarosite

Jarosite waste, originating from the zinc industry using hydrometallurgical processing routes, is considered hazardous. Metals such as zinc, cadmium a nd copper are present in an environmentally mobile form, thus the jarosite waste is usually stored in linen ponds. Autoclaving of this material with a cellulose type waste material, such as sewage sludge, with the addition of a neutralizing agent will transform most of the metals into oxides, which are immobile under neutral conditions. Jarosite waste and its treated produ ct were tested in standard column tests, as prescribed by Dutch legislation if the material is to be used as construction material. In three weeks tim e an amount of simulated rainwater, equal to ten times the weight of the so lid, was percolated through the samples. The moisture content of jarosite w aste is about 40 wt%, reflecting the leach liquor from the zinc refining pr ocess; its solutes are easily leached out. This leach liquor initially cont ained high concentrations of Zn, Cu and Cd, but when a liquid/solid ratio o f two (L/S=2) was reached most of these metals were removed from the jarosi te waste. Go-treatment of jarosite with sewage sludge yields a product whic h is far more acceptable. Even so, the leached amounts of zinc and cadmium do not match the Dutch criteria for second-grade construction material. Cou nter current washing of the residue improves its properties as a constructi on material, although the best environmental option for the solid residue i s further (thermal) treatment (Hage ct al., 1996). (C) 2000 Published by El sevier Science Ltd. All rights reserved.