Silica Geochemistry and Scaling...


Silica scaling is a special problem in geothermal power development.  Unlike many other minerals, silica can form a colloid when brines become oversaturated.  Typical silica colloids are shown above as spherical particles.  The colloids have diameters ranging from 5nm to >5000nm.  The colloid properties depend on the individual brines, and the method by which the brine became oversaturated. 

Each geothermal field is different, and therefore field-specific experiments are necessary to define the characteristics of the colloid.  We have developed special equipment to measure the polymerisation of silica t
o a colloid at any temperature and pressure.  This data is essential in defining the likelihood of silica deposition in surface plant and reinjection wells.  The equipment can also measure  the polymerisation characteristics when the pH is altered.  pH adjustment is one commonly used method of coping with silica deposition.  

In the pre-development stage, we can calculate likely silica concentrations, and the likelihood of silica deposition.  This can greatly assist in the definition of turbine inlet pressures and separation pressures.