Calcium Pyrophosphate Crystal Salt forms and the Influence of Phosphocitrate (original) (raw)
The inhibition of calcium carbonate precipitation in aqueous media by organophosphorus compounds
Journal of Colloid and Interface Science, 1992
The formation of insoluble calcium carbonate scale is often undesirable and the use of water additives which prevent or retard the deposition of this salt is widespread as the alternative solution of water acidification would cause severe corrosion problems. In the present work, the effect of four synthetically prepared compounds, 1,2-dihydroxy-l,2-bis(dihydroxyphosphonyl)ethane (DDPE), 2-dihydroxyphosphonyl-2-hydroxypropionic acid (DHHPA), 1,3-bis[( 1-phenyl-l-dihydroxyphosphonyl)methyl]-2-imidazolidinone (BPDMI), and 2,3-bis(dihydroxyphosphonyl)-l,4-butanedioic acid (BDBA), on the spontaneous precipitation of calcium carbonate in aqueous media was investigated. The precipitation process was studied in batch reactors at 25°C and pH 8.50, under conditions of sustained supersaturation. Two of the organophosphorous compounds investigated, DDPE and BDBA, contained P--C--C--P bonds in their molecules. In a third, BPDMI, the two P--C bonds were separated by a bulky fivemembered ring, and the other, DHHPA, contained only one P--C bond. All organophosphorus compounds examined in the present work were synthesized in the laboratory and were found to be resistant to hydrolysis even at elevated temperatures, typical of those existing in geothermal wells. In all cases, the induction periods preceding the onset of the spontaneous precipitation of calcium carbonate were significantly increased depending on the concentration of the additives examined, while the concomitant precipitation rates were markedly slower at concentration levels as low as 2 × 10 -8 mol dm -3. It is possible that the inhibiting effect of the organophosphorus compounds tested is due to the blocking of the active growth sites of the crystallites formed after the induction period. The existence of the P--C--C--P bonds in the molecules of the organophosphorus compounds resulted in the most effective inhibitors, while the separation of the two phosphonyl groups by the bulky five-membered ring resulted in the same inhibitory activity as with the compound possessing only one phosphonyl group.
Addition of carboxylate-containing polymeric materials to a metastable supersaturated calcium carbonate solution greatly reduced calcite crystal growth rates at constant supersaturation and pH = 8.5. Calcite crystallization rates were decreased to half their value in pure solutions by a tannic acid concentration of about 0.3 ppm (parts per million); a fulvic acid concentration of about 0.2 ppm; and a poly(acrylic acid) concentration of about 0.0175 ppm. An equation relating the calcite crystallization rate and the additive concentration follows an expression based on a Langmuir adsorption model. However, the Langmuir isotherm plot has two linear segments suggesting that these polyelectrolyte inhibitors may selectively adsorb initially at the fastest growing crystal faces. This relation between polyelectrolyte concentration and calcite growth rates implies inhibition by carboxylate-containing polymeric materials involves blockage of crystal growth sites on the calcite surface.
The use of natural hard waters in industrial water systems (e.g., cooling, boiler, desalination, oil production, etc.) can cause severe scaling and corrosion of equipment surfaces and pose serious technical and economic challenges. The scales commonly encountered are sulfates, carbonates, and phosphates of calcium, magnesium, and barium. The precipitation and deposition of scale on equipment surfaces are influenced by various factors including feed and re-circulating water chemistry, pH, temperature, flow velocity, heat exchanger metallurgy, and types of additive used in the treatment program. Such scale deposits significantly reduce heat transfer efficiency, constricts flow (e.g., reduces internal pipe diameters), increase the operating pressure of pumps, and enhance the probability of corrosion damage. In many cases, the removal of deposits leads to discontinuous operation of the system, resulting in higher operating costs. In addition, treatment chemicals (i.e., flocculants and coagulants) used upstream to treat feed water also influence the performance of additives used to prevent the precipitation of scale forming salts.
Inhibitory Effects of “Green” Additives on the Crystal Growth of Sparingly Soluble Salts.
In this chapter the effects of environmentally friendly additives on formation and growth of sparingly soluble salts are presented in a concise way. Specifically, the influence of a biodegradable, environmentally friendly polysaccharide-based polycarboxylate, carboxymethyl inulin (CMI), on the crystal growth kinetics of calcium oxalate has been studied. The spontaneous crystallization method was used to delineate the crystallization kinetics of calcium oxalate (CaC 2 O 4 , CaOx). The results demonstrate that the retardation in crystal growth is controlled by the carboxylation degree of the CMI and its concentration. These studies also show that CMI additives direct calcium oxalate crystallization from calcium oxalate monohydrate (COM) to calcium oxalate dihydrate (COD). Colloidal silica is known to be a substantial problem in silica-laden process waters. Although silica "technically" is not a salt, it is often categorized with them, as it brings about the same problems as mineral scale deposits (reduced heat transfer, etc.). We also report a strategy to retard silicic acid condensation in supersaturated aqueous solutions by using non-toxic, "green", zwitter-ionic phosphonomethylayed chitosan (PCH). An overview of the use of green additives in water treatment is also presented.
Desalination, 2020
Calcium carbonate (CaCO 3) scale deposition causes serious issues in industries which deal with water, and its formation reaction is pH-depending. This study investigated the efficiency of sodium hexametaphosphate (SHMP) as scale inhibitor for calcium carbonate, as a function of pH and SHMP concentration, under drastic conditions of temperature, scaling ions concentration and pressure. The relationship between pH and CaCO 3 formation parameters was evaluated by static and dynamic tube blocking tests and scanning electron microscopy (SEM) images. Quantum chemistry calculations were performed to evaluate thermodynamic values related to interactions between the inhibitor and CaCO 3. At pH 6.5, excellent results were found with complete inhibition of CaCO 3 deposition on capillary with just 2.5 mg L −1 of SHMP and deformed structures for CaCO 3 crystals were observed by SEM images. Results also showed a reversal behavior of SHMP as inhibitor at pH neutral and slightly alkaline, with a decrease on inhibition efficiency even raising SHMP concentration, related to the fast precipitation of CaCO 3 in the drastic conditions evaluated.
Heliyon, 2021
Scale formation is a bottleneck of most industrial and domestic water equipment, in particular, of oilfield water systems. Therefore, high-performance and environmentally-benign chemical scale inhibitors are highly needed. Phosphino-polycarboxylic acid (PPCA) is a low-in-phosphorous scale inhibitor with high inhibition efficiency, but its synthesis and performance analyses have been rarely disclosed. In this work for the first time, a PPCA copolymer is synthesized by a simple method based on free radical polymerization of acrylic acid and phosphinic acid monomers and directly employed for gypsum scale inhibition. The formation of PPCA was verified by FTIR and 31 PNMR spectroscopies, and then its inhibition performance was evaluated by the complexometric determination of the Ca 2þ concentration. The PPCA (2.5 ppm) showed 100% inhibition efficiency at a saturation index of 0.31 at the room temperature and without pH regulation after 24 h with practically no detectable gypsum crystallites even after two months, while the commercial ATMP showed a low inhibition efficiency of 30%. The Field Emission Scanning Microscopy (FESEM) images of the PPCA-inhibited and uninhibited samples revealed that the typical gypsum microfibers are distorted and reduced in size significantly in the inhibited sample. At a still higher saturation index of 1.47 (saturation ratio of 10), the inhibition efficiency of PPCA reduced to 16% and 24% for two dosages of 2.5 and 10 ppm which was attributed to the higher ion activity coefficients at the extremely high ionic strength, and hence, a much higher thermodynamic driving force. The rate constants for these two high supersaturation conditions and low PPCA dosages were also calculated and discussed.
Journal of Crystal Growth, 1988
The kinetics of crystal growth of calcium oxalate monohydrate seed crystals were investigated potentiometrically in the presence of several polyhydroxycarboxylic acids: etylenediaminetetraacetic acid, citric acid, isocitric acid, malic acid and succinic acid, and it was found that they inhibited crystal growth, except in the case of isocitric acid that manifested no-effects. An apparent rate order of 2 in the presence of all the inhibitors, suggested a spiral growth mechanism. Application to a kinetic Langmuir-type model suggested that adsorption of the polyhydroxycarboxylic acids, at the active growth sites, is the cause of the reduction in the crystal growth rates. The inhibitory action of the different substances assayed was comparatively evaluated. Relations between chemical structure and inhibitory capacity were established.
Crystal modification of calcium sulfate dihydrate in the presence of some surface-active agents
Journal of Colloid and Interface Science, 2004
The effect of surface-active agents (surfactants), as additives, on the crystallization of gypsum was studied under conditions of the simulated dihydrate process of phosphoric acid production. Calcium hydrogen phosphate and sulfuric acid were mixed with dilute phosphoric acid at 80 • C, and the turbidity of the reaction mixture was measured at different time periods to determine the induction time of gypsum crystal formation. Two types of surfactants, namely, cetyltrimethylammonium bromide (CTAB) as a cationic surfactant and sodium dodecyl sulfate (SDS) as an anionic surfactant were added to investigate their effects on the crystallization of gypsum. Addition of CTAB decreased the induction time and increased the growth efficiency, while addition of SDS increased the induction time and decreased the growth efficiency compared with the baseline (without additives). The surface energy increased with CTAB and decreased with SDS compared with the baseline. The percentage of fine crystals decreased in the presence of CTAB and increased in the presence of SDS compared with the baseline. Gypsum morphology changed from needle-like in the absence of additives to tabular in the presence of CTAB.