The evaluation of the effect of a buffered HCl-HF acid solution on the removal of silica in geothermal scales

• Main Authors: Butalid, Nicole Elene Sanz, Chua, Kendreck Lim, Rivera, Alberto Ong
• Format: text
• Language: English
• Published: Animo Repository 1997
• Subjects: Buffer solutions; Acid-base equilibrium; Silica; Solution (Chemistry); Incrustations; Pipes, Deposits in; x5 Water-formed scale deposits; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_bachelors/6444
• Institution: De La Salle University

Of growing importance in geothermal and petroleum industries is the silica deposition on equipment as temperature is reduced and evaporation occurs. In normal practice in these industries, these deposits are removed with an HCI-HF acid mixture. However, the problem of reprecipitation surfaces since the pH is not maintained and silica redeposits. This study deals with an analysis of the amount of silica scale removed using a buffered HCI-HF acid solution. Since buffers are an effective method of pH control, a buffered solution would then eliminate reprecipitation and thus have silica remain in solution. The performance of two buffers was evaluated against the performance of a bufferless solution on the scales. The goals of this study are (a) to analyze if increasing acid concentration has a significant effect on the removal of silica in silica scales (b) to analyze if particle size contributes significantly to the removal of silica in silica scales and (c) to analyze the effects of using a buffer in the solution. Results show that increasing the % HCl-concentration (for buffered systems) and the particle (mesh) size to the specified amounts bear no significant effects on the amount of silica scale removed. However, increasing the % HF concentration shows significant effect on the amount removed, with the amount removed increasing as the % HF increases. Furthermore, the pH level was found to have an effect on the amount of scale removed, with the highest amount removed at the pH-level at or near the pKa value of the buffer. From these results it was found that the performance of a buffered system is better than the unbuffered because (a) the buffered system can effectively maintain the pH of the solution, and (b) buffered systems eliminate the need for HCL since it was shown that 0% HCL can accomplish the same amount of scale removed as a 9% HCL.