The width of metastable zone of unseeded potassium alum solutions was determined for different conditions and in the presence of additives. The measurements were taken at three different cooling rates and for three different saturation temperatures at a cooling rate of 10 K/h by means of an ultrasonic measuring technique. The influence of Cr 3+ , Cu 2+ , and Mg 2+ ions on the width of metastable zone of a potassium alum solution was investigated at a cooling rate of 5 K/h. The influence of Mg 2+ ions on the width of metastable zone of potassium chloride solutions was also investigated at a cooling rate of 10 K/h. Cr 3+ , Cu 2+ , and Mg 2+ ions show both enlargement and suppression effects on the width of metastable zone of potassium alum and potassium chloride solutions depending on their concentrations. Cr 3+ , Cu 2+ , and Mg 2+ ions also change the saturation temperature of potassium alum solutions depending on their concentrations.

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The crystallization of Calcium sulfate dihydrate produced by the reaction between pure Ca(OH) 2 suspension and H 2 SO 4 solution was investigated at different pH values, temperatures and citric acid concentrations. Crystal size distributions, filtration rates and zeta potentials of gypsum were determined as a function of citric acid concentrations at pH 3.5 and 65°C. The influence of citric acid on the morphology of gypsum was also investigated and discussed. The average particle size of gypsum was reached to maximum in the presence of approximately 2500 ppm citric acid concentration, where the minimum cake resistance and maximum filtration rate were obtained. In the presence of citric acid, various crystal morphologies such as tabular, platelike, double-taper leaf-like and flower-like, etc., were obtained. The change of morphology is related to the preferential adsorption of citric acid on different crystallographic faces.

Reactive crystallization of calcium oxalate was investigated in the presence of amino acids, proteins and carboxylic acids at different pH and temperatures. Average particle size, filtration rates of calcium oxalate crystals obtained in the absence and presence of additives were determined. The influence of pH, temperatures and additives on crystal morphology of calcium oxalate were also investigated and discussed by SEM analysis. TG-DTA, FT/IR and XRD analysis were carried out for all investigated conditions. Average particle size of calcium oxalate was affected significantly by the additive type and concentration. Variation of crystal morphology depending on type and concentration of the additives affected the filtration characteristics. Majority of calcium oxalate crystals occurred in the form of calcium oxalate monohydrate except those in the presence of tartaric acid. TG-DTA, FT/IR and XRD analysis proved that calcium oxalate monohydrate and calcium oxalate dihydrate mixtures are formed in the presence of tartaric acid. The effect of all additives on scale formation was also investigated.