Transport of Cr(VI), Ni(II) and Mn(II) through metallurgical wastes.: Batch and column experiments

The adsorption/desorption processes in metallurgical wastes of Cr, Ni and Mn in single, binary and ternary solutions were investigated using batch tests and miscible displacement column experiments. For the experiments, mine wastes from Moa (Cuba) composed by oxi(hydroxi) iron minerals and heavy metals deposited in tailing dams were used. The adsorption isotherms of the three metals are strongly non-linear and are well described by the Freundlich isotherm. Desorption isotherms are linear. The adsorption/desorption process of Cr, Ni and Mn shows hysteresis. The adsorption of metals can be attributed to the favourable electrostatic interaction due to mineralogical composition of the wastes. The shape of breakthrough curves from column experiments provide evidence that transport of Ni, Mn and Cr is non-ideal with asymmetry and great tailing, showing an important retardation relative to a tracer. When using a ternary solution (Cr, Ni, and Mn), retardation of Ni and Mn was reduced in comparison with the single solute experiment, consequence of the NI and Mn competition for adsorption sites, while Cr did not show any change. In the Ni-Mn binary solution column transport experiment, Mn adsorption was more rapidly attained than Ni; and both metals show different adsorption behaviour, when adsorption of Ni increases, sorption of Mn decreases. One more aspect being investigated was the sorption capacity of the metallurgical waste. According to the mass-balance analysis of the results, the waste shows a very high effective sorption.