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51316-7039-Silica Removal By A Novel Electrochemical System

Picture for Silica Removal By A Novel Electrochemical System
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Product Number: 51316-7039-SG
ISBN: 7039 2016 CP
Author: David Hasson
Publication Date: 2016
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D. Hasson O. Gorni-Pinkesfeld H. Shemer R. Semiat The presence of silica in brackish water greatly complicates desalination processes. Threshold limits for silica deposition are rather uncertain and the complex mechanisms involved are not well understood. Scale control is usually achieved by dosage of anti-scalants. However mitigation of silica scale has proved to be an elusive task. The common method of silica removal is by precipitation with polyvalent metal hydroxides at high pH. A convenient way for achieving alkaline pH is by using an electrochemical cell. The high pH on the cathode surface induces silica precipitationon its surface. Silica removal was investigated using a novel technique based on an electrochemical cation exchange membrane system (ECM system). The basic concept of the ECM system is separation of the anode and cathode compartments by the cation exchange membrane and precipitation in a separate crystallization vessel. The ECM system overcomes major drawbacks of current electrochemical technology notably high electrode area requirements enabling considerable reduction of the cathode area by a factor of 10 to 20. The objective of this study was to analyze the silica problem from both fundamental and practical aspects. The effects of current density and pH on the silica precipitation rate and on its fractional removal were studied. Electrochemical silica removal from brackish waters by the novel system confirmed that the presence of magnesium was essential for silica elimination with the highest removal occurring at the optimal molar ratio of 4:1 Mg to SiO2. The experimental results supported the hypothesis that silica removal was an adsorption process rather than a chemical precipitation reaction. Silica depletion was found to increase with current density reaching an asymptotic limit of 92% at a solution pH of 10.8 achieved by a current density of 200 A/m2. Results of this work indicate that silica removal by the ECM system is a viable process.
D. Hasson O. Gorni-Pinkesfeld H. Shemer R. Semiat The presence of silica in brackish water greatly complicates desalination processes. Threshold limits for silica deposition are rather uncertain and the complex mechanisms involved are not well understood. Scale control is usually achieved by dosage of anti-scalants. However mitigation of silica scale has proved to be an elusive task. The common method of silica removal is by precipitation with polyvalent metal hydroxides at high pH. A convenient way for achieving alkaline pH is by using an electrochemical cell. The high pH on the cathode surface induces silica precipitationon its surface. Silica removal was investigated using a novel technique based on an electrochemical cation exchange membrane system (ECM system). The basic concept of the ECM system is separation of the anode and cathode compartments by the cation exchange membrane and precipitation in a separate crystallization vessel. The ECM system overcomes major drawbacks of current electrochemical technology notably high electrode area requirements enabling considerable reduction of the cathode area by a factor of 10 to 20. The objective of this study was to analyze the silica problem from both fundamental and practical aspects. The effects of current density and pH on the silica precipitation rate and on its fractional removal were studied. Electrochemical silica removal from brackish waters by the novel system confirmed that the presence of magnesium was essential for silica elimination with the highest removal occurring at the optimal molar ratio of 4:1 Mg to SiO2. The experimental results supported the hypothesis that silica removal was an adsorption process rather than a chemical precipitation reaction. Silica depletion was found to increase with current density reaching an asymptotic limit of 92% at a solution pH of 10.8 achieved by a current density of 200 A/m2. Results of this work indicate that silica removal by the ECM system is a viable process.
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