THE INFLUENCE OF HYDROLYZABLE METAL-CATIONS ON THE ELECTROKINETIC BEHAVIOR OF TIN TAILINGS SLURRY

The profound influence of the hydrolytic behaviour of ions of heavy metals such as Cu, Zn, Pb, Cd, Mn and Ni on the electrophoretic mobility of colloidal clay taken from slurries from ponds from former tin mines was studied. The strong adsorption of soluble hydrolysed species and insoluble metallic hydroxide on the clay surface leads to a reduction in the surface charge of the day particles and eventually to charge reversal. The results show that the shape of the mobility-pH curves was completely different from those for simple cations. Generally, at concentrations greater than 10(-4) mol dm(-3) and pH > 6, the metal ions hydrolyse extensively to form positively charged mononuclear and polynuclear species which could become adsorbed and reverse the charge of the clay particles. At higher pH, a second reversal, back to negatively charged surface, occurred owing to the formation of insoluble metal hydroxide. At very low concentration of metal ions, two constant (negative) mobility regions were observed: one under acidic pH and the other under alkaline pH. The hydrolysis was influenced by the presence of particulates in the systems.