Uptake of dissolved arsenic during the retrieval of silica from spent geothermal brine

A study has been made on the uptake of dissolved arsenic in a recirculation system designed to extract silicates for secondary use from spent (i.e. cooled) geothermal brine. Excess dissolved calcium, due to addition of lime (CaO), favours the precipitation of As-bearing phases in the retrieved materials. Controlling dissolved calcium in a continuous recirculation system is not easy to achieve; arsenic removal prior to precipitation of silicates is expected to be more practical. Predicted and measured arsenic speciation in the spent geothermal brine is dominated by arsenite species that were previously shown to lack affinity with most inorganic sorbents. However, synthetic schwertmannite was able to selectively remove dissolved arsenic without any significant accompanying decrease in silica concentrations. Its use prior to the introduction of spent geothermal brine into the recirculation system will likely make silica retrieval more feasible.