Based on the silicate content in geothermal water，adjusting the addition amount of scale inhibitors can prevent the formation of silicate scale on the surface of returning pipes in the deep underground. Consequently, an automatic system for determining the high-concentration silicate was proposed. This analytical process was as follows. First, NaOH solution mixed with a sample of geothermal water in premixing coil to make polymeric silicon translate into active silicon like H4SiO4 and SiO32-.And then volumes of the sample and a chromogenic agent were measured simultaneously and automatically, injected into two carriers, merged and reacted in a reaction coil in manner of the reagent enwrapping the sample. Formed product entered into a masking coil of eliminating interferences and a flow detector in turn, and was determined under the wavelength of 405 nm. Optimized conditions were as follows: Concentrations of ammonium molybdate, NaOH and oxalic acid were 2% (w/v), 0.1 mol·L-1,and 1% (w/v), respectively,lengths of premixing, reacting and masking coils were 350, 510, and 300 cm, respectively; the total flow rate was 5.0 ml· min-1.This method only consume 25 μl of the sample and 115 μl of the chromogenic reagent per time, its determination range was 25~800 mg·L-1(SiO2),relative standard deviation was less than 0.81%, recovery ranges were 96.2%~117.0%, about 180 samples can be analyzed per hour. Merits of the system were good reproducibility, high analysis speed, less test cost, and not needing to predilution for determination of high concentrations silicate. The most important was that it realized continually monitoring of the high concentration of silicate in the geothermal water.
