Effects of pH and Ca/P molar ratio on the quantity and crystalline structure of calcium phosphates obtained from aqueous solutions

Abstract

et al.. Effects of pH and Ca/P molar ratio on the quantity and crystalline structure of calcium phosphates obtained from aqueous solutions.Abstract -Milk and dairy products contain large amounts of calcium phosphate salts that can precipitate. The chemical composition and the crystalline structure of the calcium phosphate precipitates that are formed in dairy industry depend on the physico-chemical conditions, particularly, pH and mineral composition. The objective of this study was to determine, using mineral solutions, the effects of pH and of the concentrations of calcium and phosphate on the quantity and crystalline structure of calcium phosphate precipitates. Experiments were carried out at 20°C with 20.00 mmol·L −1 phosphate and three Ca/P molar ratios (1.00, 1.50 and 2.00). The initial pH (5.50, 6.70, 7.50, 8.50 and 9.50) were drifting or kept constant during a reaction time of 3 h. After filtration of the suspensions, the mineral compositions of filtrates were quantified. The lyophilized precipitates were characterized using X-ray diffraction, infrared spectroscopy and scanning electron microscopy techniques. At drifting pH (final pH values were between 4.6 and 6.0), the mineral analyses showed that the Ca/P ratio did not influence the amounts of precipitated calcium and phosphate. The analyses of precipitates revealed the formation of brushite as the main crystalline phase. At constant pH, the mineral analyses showed that the Ca/P ratio strongly influenced the precipitation efficiency of calcium phosphate. The analyses of precipitates revealed the formation of poorly crystallized calcium-deficient apatites. A decrease of crystallinity with an increase in initial pH was observed. In conclusion, pH can be a key factor to control the quantity and crystalline structure of calcium phosphates obtained by precipitation. This factor should be considered for the recovery of calcium phosphates from dairy co-products. pH is also important in the fouling phenomena of membranes and heat exchangers caused by calcium phosphate precipitation. milk / dairy product / calcium phosphate / precipitation / brushite 摘要 -pH 和 Ca/P 摩尔比对磷酸钙的产量和晶体结构的影响○ 乳和乳制品中含有丰富的、 可 沉淀的磷酸钙○ 从乳制品中获得磷酸钙沉淀的化学组成和晶体结构完全决定于发生反应的物 理和化学条件，特别是 pH 和矿物元素的组成○ 通过调整 pH、钙浓度和磷酸盐浓度，研究 这些因素对生成磷酸钙沉淀的产量和晶体结构的影响○ 在 20°C 下，20.00 mmol·L À1 的磷酸 盐和 3 组不同 Ca/P 摩尔比的溶液

Modelling ion composition in simulated milk ultrafiltrate (SMUF). I: Influence of calcium phosphate precipitation

“…The formation of calcium phosphate precipitates depends on environmental conditions such as pH, ionic strength, temperature, molar ratio of Ca/P, presence of other ions (Johnsson & Nancollas, 1992;Schmidt, Both, Visser, Slangen, & Vanrooijen, 1987;Spanos et al, 2007;Van Kemenade & De Bruyn, 1987). Earlier studies (Johnsson & Nancollas, 1992;Mekmene et al, 2009;Van Kemenade & De Bruyn, 1987) have shown that pH is the key factor that determines the crystalline structure of calcium phosphates. DCPD and OCP are formed in more acidic conditions, whereas HAP is preferentially formed under neutral or basic conditions.…”

Physicochemical characterisation of calcium phosphates prepared from milk ultrafiltrates: Effect of the mineral composition

“…These results are in agreement with those obtained by Anema (2009) on industrial MDCP precipitates. In previous study, we showed the formation of poorly crystallised calcium deficient apatites (CDA) from aqueous solutions containing Ca and P i ions (Mekmene et al. 2009a).…”

“…1977; Madsen and Thorvardarson 1984; Nancollas 1990; Madsen and Christensson 1991; Guo et al. 2005; Mekmene et al. 2009a).…”

“… Model solutions containing Ca and P i (Schmidt and Both 1987; Van Kemenade and De Bruyn 1987; Tsuge et al. 2002; Mekmene et al. 2009a).…”

Effect of the Chemical Composition of Simulated Body Fluids on Aerogel-Based Bioactive Composites

“…The reason for this can be the strong basic character of β-tricalcium phosphate, which can cause a change in the pH of the simulated body fluid in the vicinity of the tricalcium phosphate (TCP) particles. Furthermore, it is well known that the solubility of the calcium phosphates decreases at higher pH [55]. Thus, if the pH is high enough in the nearly supersaturated solution, spontaneous crystal formation can occur even if the sintered silica aerogel matrix reduces the number of the calcium binding sites.…”