Date of Award

Winter 1989

Project Type

Dissertation

Program or Major

Engineering

Degree Name

Doctor of Philosophy

First Advisor

Michael Collins

Abstract

Aluminum salts are the most common coagulants used in water treatment to remove contaminants. The objectives of this research was to provide an understanding of some aspects of the influence of sulfate in aluminum coagulation chemistry of natural water. Al(III) solutions were titrated with base to study the role of sulfate in the hydrolysis/precipitation of aluminum. Jar tests were conducted to treat water samples containing varying concentrations of aquatic humic substances (AHS), sulfate and pH. The kinetics and adsorption isotherms of sulfate and aquatic humic substances on aluminum precipitate were developed in adsorption experiments using aluminum precipitate adsorbents. The application of a sensor for Al(III) based on immobilized morin was investigated. Aluminum chloride and aluminum nitrate had similar hydrolysis/precipitation characteristics. Aluminum precipitation occurred at a lower formation function ratio r = (OH) $\sb{b}$/ (Al) $\sb{t}$ for aluminum sulfate than for aluminum chloride or aluminum nitrate. The aluminum sulfate precipitate was presumed to be an Al-OH-SO$\sb4$ solid. Equilibrium calculation (ALCHEMI) predicted jurbanite for similar conditions. The addition of sulfate to aluminum chloride solutions resulted in titration curves similar to that of aluminum sulfate. Acidification of the sample prior to titration did not impact the titration curves. An aluminum speciation scheme was presented showing the predominance of monomers at low r ratios, followed by polymers, and Al(OH)$\sb4\sp-$ at high r ratios. pH had the most influence in the coagulation of the water samples treated. The impact of sulfate and AHS additions varied depending on the pH. Turbidity and AHS removal were greater at pH4 than at pH7. Maximum removals were obtained at pH5.5. The formation function fell within the range measured in the Al(III) titration experiments. Higher aluminum precipitates were measured at pH7. The adsorption data of aquatic humic substances (AHS) on aluminum chloride and aluminum sulfate precipitates fitted the Freundlich isotherm best. More AHS adsorbed to the aluminum sulfate precipitate. Little difference existed between the AHS absorbed to either aluminum chloride or aluminum sulfate at pH5.5 and 7. AHS adsorbed to aluminum precipitates formed with AHS. Sulfate adsorption on aluminum precipitates increased with decreasing pH and fitted the Langmuir isotherm best. The competition between AHS and sulfate for the adsorption sites of the aluminum precipitates favored AHS. Inconsistent results were obtained with the sensor based on immobilized morin. Modifications to the procedure and the use of other ligands were recommended in lieu of morin.

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