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Environmental Engineering Research 1997;2(1): 21-31.
Roles of Molar OH/Al Ratios in Al-Based Salts on Neutralizing Particle Surface Charges for Coagulation
Jong Woon Kwak
Environmental Laboratory, Kyunggi Chemical, Seoul, Korea
Corresponding Author: Jong Woon Kwak ,
Received: July 8, 1996;  Accepted: December 9, 1996.
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The molar OH/Al ratios in aluminum salts influenced greatly the capability to neutralize the particle surface charges in a suspension. The increase of value in OH/Al allowed the more decrease in the thickness of electrostatic double layer of particle surfaces. The sizes of floe formed by Al salts were continuously measured with time in a system during flocculation, demonstrating that the high ratio of OH/Al favors the bigger floe formation. Also, metastable aluminium species seemed to be a efficient tool to form a good floe in a time frame and further to give an improved settleability. Chemical precipitation of both suspended solids and non-ortho-phosphates from sewage water were enhanced with increasing OH/Al ratios, but rather ortho-phosphorous removal was decreased, representing that it is more selective to an ionic reaction with aluminum. An aluminum salt with OH/Al=234 was well suited to the formation of uniform floes, resulting in the more rapidly settling rate. Also, a degree of neutralization of particle surface charges was more enhanced with increasing mixing speed, as well as with OH/Al molar ratio of coagulant The structural properties of aluminum consisting of coagulants were characterized by X-ray diffraction.
Keywords: Coagulant | Basicity | OH/Al Ratio | Suspended Solid
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