Antimony and Arsenic Sulfide Scaling in Geothermal Binary Plants

Abstract

With the advent of acid dosing for silica scaling control, and the increased utilisation of binary plants, the incidence of antimony sulphide scaling has become a concern. To a much lesser extent, arsenic sulphide scaling can also occur under similar circumstances. The combination of lower brine temperatures and lower pH can lead to significant antimony sulphide scaling. Although the antimony concentration in the brine can be very low, antimony sulphide scaling can become almost quantitative. This can lead to loss of heat transfer in binary plant heat exchangers, and injectivity decline in reinjection wells. Recent work has produced averaged thermodynamic data that seems to better predict the onset of stibnite scaling. Present options for remediation include caustic soda washing, steam cleaning and mechanical removal.