Effect of silica polymerisation and pH on geothermal scaling

Abstract Siliceous scales were formed under controlled conditions from geothermal discharge waters, in contact with air, flowing over ceramic tiles and through steel pipes. Waters were aged for different periods, resulting in different degrees of polymerisation of silica. Ageing discharge waters from Broadlands and Wairakei (in New Zealand) was not an effective method for reducing the amount of scale formed; however the physical appearance of the scales could be changed by ageing. Water at normal pH (7·5–9) was also compared with water acidified to a pH of about 4. The acidified discharge water formed scales up to one hundred times slower than untreated water. It is suggested that acidification may be a practical method for minimising scale formation.