Biomass-clay complexes for Sr2+ and Co2+ removal: New insights on sorption and separaation properties of the sorbents

Abstract

Co2+ and Sr2+ sorption capacity of an argentine montmorillonite (MMT) and two biomass-clay complexes (BMMTs) was determined, evaluating the available sorption sites and the coagulation/flocculation properties in the absence and presence of Co2+ and Sr2+. BMMTs presented higher Co2+ sorption capacity than MMT (0.25 mmol/g vs. 0.17 mmol/g). No significant differences on Sr2+ removal were observed among the sorbents (0.18 mmol/g), associated with the higher Sr ionic radius, which could hind its sorption compared to Co. The sorption of these heavy metals occurs on both, internal and external surfaces of MMT and BMMTs. In pollutants absence, MMT generates stable colloidal suspensions, while BMMTs flocculated spontaneously. However, in pollutants presence, MMT decanted faster than BMMTs, probably related with two factors: (i) the reduction of the surface electric charge due to the pollutant sorption, which reduce the electrostatic repulsion of clay grains and allows their coagulation and posterior flocculation and (ii) the presence of micro swirls generated around BMMT by the fungi filament, which produces an increase on the buoyancy force followed by a decrease on the net force toward the bottom. The relatively fast coagulation/decantation of MMT (after 2.5 h half of MMT particles were in the bottom) could cause an inefficient sorption process considering the optimal time needed for pollutant sorption, around 4 h. BMMTs remained in suspension the enough time, promoting an optimal sorption. These studies allow the development of an efficient and affordable remediation process for the treatment of wastewaters contaminated with radionuclides.