Title:

Predicting the Precipitation of Amorphous Silica from Geothermal Brines

Authors:

Oleh Weres, Andrew Yee, and Leon Tsao

Conference:

Stanford Geothermal Workshop

Year:

1978

Session:

Modelling

Language:

English

File Size:

156KB

View File:

Abstract:

The voluminous gel-like deposits encountered at Cerro Prieto, Wairakei, anti Ni1 and consist of flocculated colloidal amorphous silica. The crumbly grey and white scales associated with the gel-like materials are cemented colloidal aagregates. This colloidal silica is produced by homogeneous nucleation in the liquid phase; i.e., nucleation by growth of polymers to critical nucleus size without the participation of some preexisting solid particle.

With most substances heterogeneous nucleation is dominant, and homogeneous nucleation is very slow, rare in nature, and difficult to study in the laboratory. The precipitation of amorphous silica is an apparent exception to this because of the very low surface tension of the silica- water interface - between 35 and 50 ergs cm-2 over the range of major practical interest. (By comparison, the surface tension of the water-air interface is about 70-80 ergs cm-2.) This means that enormous numbers of particles can be produced by homogeneous nucleatioln (on the order 1017 to 10l8 per liter ), and this completely swamps the effects of heterogeneous nucleation.

A practical consequence of the dominance of homogeneous nuceation is that the precipitation of amorphous silica is experimentally reproducible and predictable. is determined by basic thermodynamic and chemical variables (concentration, surface tension, etc.) and not by often unknown trace contaminants as is the case with heterogeneous nucleation.


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