Comparison of strontium and calcium adsorption onto composite magnetic particles derived from Fe3O4 and bis(trimethoxysilylpropyl)amine

The adsorption of strontium and calcium ions by composite magnetic particles derived from Fe3O4 and bis(trimethoxysilylpropyl)amine (TSPA) were comparatively studied. The effects of initial solution pH, ionic strength, initial strontium and calcium ion concentration, and temperature on the equilibrium adsorption amount of both strontium and calcium ions, and on the separation factor between strontium and calcium ions were investigated comprehensively. The adsorption occurs rapidly in the first 30 min. In general, the equilibrium adsorption amount of both strontium and calcium ions was found to increase with the increase in initial ion concentration and initial solution pH, but to decrease gradually with the increase in ionic strength. The equilibrium adsorption amount of strontium ions increases with the increase in adsorption temperature. However, the effect of temperature on the adsorption of calcium ions presents a complicated situation. Strontium ions have a higher affinity to the composite particles than calcium ions. The separation factor between strontium and calcium ions increases with the increase in adsorption temperature, but is not sensitive to ionic strength. The suitable experimental conditions for the separation between strontium and calcium ions are: initial solution pH 7–8, lower ionic strength, and higher adsorption temperature.