Activated silica sol as a flocculant in treatment of mine effluents

Lime neutralization of acidic drainage is the most common process to produce an environmentally acceptable effluent. The process involves neutralization, precipitation of metal hydroxides, flocculation, settling and storage of the sludge. The sludge is not entirely stable over the long term due to the natural pH decline in the storage area that can re-solubilize metals. The use of activated silica sol could be an alternative to flocculants in the lime neutralization process. The nature of the metal hydroxide---silica bond could make the sludge more stable on short and long term.; It was observed that similar settling characteristics can be obtained with the standard flocculant and a low dosage of activated silica sol. Using activated silica sol, the settling rate is dependent on the concentration of magnesium and iron in the mine effluent.; There was an improvement in sludge stability when using a high dosage of activated silica sol. Two mechanisms have a role in the increased stability: the adsorption bond and the buffering capacity of activated silica sol. The tests suggested that a dosage of 0.1 gSiO2/gFe optimizes the settling characteristics and the sludge stability.