Removal of arsenic from geothermal water by high gradient magnetic separation

On-site experimentation of high gradient magnetic separation (HGMS) for arsenic removal from geothermal water has been conducted using a high-T_c superconducting magnet. This development of an effective method for decontamination of geothermal water is currently being done at the Kakkonda geothermal power plant in Shizukuishi, Iwate, Japan. In order to enhance the magnetic properties of the arsenic-containing particles in geothermal water, three different pretreatment methods were used: (I) the ferrite formation method; (II) the ferric hydroxide coprecipitate method; and (III) the modified ferric hydroxide coprecipitate method. The conditions of the HGMS experiments were a 1.7 T applied magnetic field and 100°C water at a flow rate of 10 L/min. Percentages of the arsenic-removal were strongly dependent on the pretreatment methods, because of a very small magnetization of the arsenic. Arsenic-removal rates of 40%, 80%, and 90% were obtained by pretreatments I, II, and III, respectively. Although the environmental standard for arsenic is 0.01 mg/L, corresponding to a 99% removal rate, could not be achieved in the present experiments, it can be thought that HGMS substantiates the achievement of environmental standards for arsenic, if an optimized pretreatment method is taken.