Manufacture of Silica Sols from Separated Geothermal Water

Abstract

A purpose built pilot plant was constructed at the Wairakei Power Station to investigate the possibility of producing silica sols from geothermal water. The plant constructed was designed to process approximately 5000 litres per hour of geothermal water and consisted essentially of a heat exchanger, several aging tanks in series and a three stage ultrafiltration module. Provision was also made for chemical injection, for washing geothermal contaminants (diafiltration) from the concentrated sol and for independent control over the variables which determined not only the silica colloid particle size, but also the concentrated silica sol stability and final concentration. Trials carried out during 1996 demonstrated that: ï Silica sols could be produced with predetermined particle sizes between approximately 10 and 70 nm and at concentrations up to 50% depending upon particle size ï Organic stabilising agents were essential to avoid gel formation ï Ultrafiltration provided a simple and efficient means of concentrating silica sols with reasonable down time for cleaning. ï Silica sols equivalent in particle size and quality to commercial silica sols can be produced successfully from Wairakeiís separated geothermal water.