Impact of colloidal iron hydroxide and colloidal silicon dioxide on calcium sulfate crystallization in the presence of antiscalants

The influence of colloidal solid nanoimpurities in water samples on scale deposition and antiscalant activity is currently gaining an increasing interest worldwide. Thus, the influence of artificially implemented iron hydroxo/oxide and silicon dioxide nanodispersions on gypsum crystallization kinetics from supersaturated aqueous solutions (0.11 mol center dot dm-3) in the presence of two industrial antiscalants of different nature: polyacrylate (PAA, AMETEK PO-2) and aminotris(methylenephosphonic acid) (ATMP, AMINAT K) is studied by a combination of methods including electro conductivity measurements at 25 degrees C, followed by SEM-EDS and powder X-ray diffraction analysis of deposits. It is demonstrated that both PAA and ATMP taken in dosages of 10 mg center dot dm-3 provide an efficient gypsum scale inhibition, increasing induction times from less than 1 minute in a blank experiment up to 100 and 70 minutes, respectively. At the same time, colloidal iron hydroxide or colloidal silicon dioxide particles artificially implemented into gypsum-antiscalant systems are found to terminate the antiscaling ability of both PAA and ATMP. The enhancement of calcium sulfate deposition by colloids is explained by: (i) an increase in the number of crystallization centers, and (ii) consumption of the antiscalant (PAA, ATMP) due to its sorption on the nanosorbent added. It is demonstrated that the induction time is likely to reflect not a scale-antiscalant interaction, but the interaction of the antiscalant with nanoimpurities. It is shown that at least in the case of calcium sulfate deposition, different solid impurities disable different antiscalants to varying degrees. This makes a thorough control of solid nanoimpurities content in water treatment technologies very desirable. Besides, the sufficient difference between induction times detected via conductivity and turbidity has been found. The induction times, registered by conductivity, appear to be larger than those indicated by turbidity. At the same time, the tind values, measured for ATMP and PAA by conductivity and by turbidity, are conflicting each other. According to conductivity, the antiscaling efficacy of PAA is higher than that of ATMP, while turbidity reveals the opposite sequence. Taking this fact into account, one has to consider the calculations of specific free surface energy absolute values for sparingly soluble salts based on induction time measurements as rather arbitrary.

Automated summary

This study investigates the influence of colloidal solid nanoimpurities in water samples on scale deposition and antiscalant activity. The results demonstrate that artificially implemented iron hydroxo/oxide and silicon dioxide nanodispersions terminate the antiscaling ability of two different antiscalants. The introduction of colloids enhances calcium sulfate deposition by increasing the number of crystallization centers and consuming the antiscalant. The induction time reflects the interaction of the antiscalant with nanoimpurities, rather than the scale-antiscalant interaction.