At Olkaria Geothermal field, Naivasha, Kenya, silicic acid and aluminum precipitation in geothermal water was investigated through batch experiments and immersion of test pieces in flowing geothermal water. This was done through a polymerization experiment by spectrophotometrically measuring monosilicic acid and reactive aluminum concentrations while their total concentrations were analyzed by ICP OES. In addition, an adsorption experiment was carried out using silica gel to act as a model of silica particles to monitor the adsorption behavior of silicic acid and aluminum on the surface of silica particles in actual geothermal water. The polymerization and adsorption experiment results are presented from three sites, OW 38 and OW 24 in the Olkaria east sector and OW 915A in the Olkaria domes. The concentration of Si-M and Si-T decreased rapidly in the first 20 minutes of the experiments, signifying rapid M-P interactions. The concentration of Al-R also rapidly decreased during this period, showing the reaction of a mononuclear aluminum species, in this case, aluminum hydroxide with silica acid, which increased the rate of precipitation of silica. A graphing of this data based on the rate law equation showed that the reactions were of second order, which confirms that probably two first-order reactions could be prominent here: Al adsorption on silicic acid and the condensation polymerization of monosilicic acid. Fe was seen not to influence the precipitation rate in these experiments as the concentration was constant in all the experiments. Large-sized colloids were also seen to be forming at an early stage via aggregation of the nano colloids that rapidly formed at this highly alkaline condition. Molecular deposition was evidenced by high silica deposition in a very short time on test pieces that were placed on the two-phase sampling valves.

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