Investigation of the Effect of a Flocculent of Bentonite Clay with MgCO3 in Synthetic AMD Treatment

Oupa I. Ntwampe* and Moothi K

Department of Chemical Engineering, University of Johannesburg, Doornfontein 2028, JOHANNESBURG, SOUTH AFRICA

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Effect of a flocculent of bentonite clay with MgCO3 in Synthetic AMD was investigated in present study. The AMD samples were collected from the western decant in Krugersdorp, South Africa was modified by adding arsenic, zinc and cobalt. The pH, conductivity, dissolved oxygen (DO), oxygen reduction potential (ORP) and turbidity were measured. Those samples were treated with bentonite clay, MgCO3 and a flocculent of bentonite clay and MgCO3 respectively in a jar test, employing either rapid or slow mixing. Results showed that the conductivity of the samples with increasing bentonite clay while keeping MgCO3 constant decreased with increasing dosage, which was attributed to adsorption of the ions onto the negative sites of the porous bentonite when ionic strength increased. The oxygen content of the DO and ORP was not influenced by the rate of mechanical agitation, i.e. rapid and slow mixing respectively. Destabilization-hydrolysis was not influenced by the pH but the ionic strength of the colloidal AMD suspension, valence and electronegative of the metal ions. Turbidity removal of the synthetic flocculent used occured through physico-chemical phenomenon (SEM micrographs) and charged porous bentonite clay. In conclusion: Bentonite clay controls equilibrium state of the ionic strength of the system through adsorption of excess ions added to the system. Velocity gradient induced by mechanical agitation does not have an influence on the turbidity removal.

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