Several beaker tests for the recovery of oversaturated silica in geothermal brines were performed with cationic precipitants to prevent silica scale deposition at the Takigami and Sumikawa geothermal plants. The reaction was studied from the start of the experiment (NRT, no retention time) and for 15 min retention time (15RT) at 90 degrees C. The silica concentration at 15RT was 200 mg/L lower than at NRT. These results indicate that the cationic flocculant reacts with polymeric silica rather than with monomeric silica and that 50 mg/L of the cationic flocculant is sufficient to reduce the silica concentration.