Calcium Colloidal processing

Two nucleation processes important to many people (including some surface scientists ) occur in the formation of gallstones in human bile and kidney stones in urine. Cholesterol crystallization in bile causes the formation of gallstones. Cryotransmission microscopy (Chapter VIII) studies of human bile reveal vesicles, micelles, and potential early crystallites indicating that the cholesterol crystallization in bile is not cooperative and the true nucleation time may be much shorter than that found by standard clinical analysis by light microscopy [75]. Kidney stones often form from crystals of calcium oxalates in urine. Inhibitors can prevent nucleation and influence the solid phase and intercrystallite interactions [76, 77]. Citrate, for example, is an important physiological inhibitor to the formation of calcium renal stones. Electrokinetic studies (see Section V-6) have shown the effect of various inhibitors on the surface potential and colloidal stability of micrometer-sized dispersions of calcium oxalate crystals formed in synthetic urine [78, 79]. 

Flocculation or clarification processes are solids-liquid separation techniques used to remove suspended solids and colloidal particles such as clays and organic debris from water, leaving it clear and bright. Certain chemicals used (such as alums) also exhibit partial dealkaliz-ing properties, which can be important given that the principal alkaline impurity removed is calcium bicarbonate—the major contributory cause of boiler and heat exchanger scales (present in scales as carbonate), although closely followed by phosphate. 

Products of this type seem to protect the humus from rapid incorporation into new biological processes. Additional factors that appear to be associated with the accumulation of organic matter in Mollisols are high exchange capacities, saturation with calcium, an abundance of mineral colloids and a high content of minerals of the smectite group (Fenton, 1983). 

Occasionally, the phosphate slime is difficult to settle in the lagoons because of its true colloidal nature, and the use of calcium sulfate or other electrolytes can promote coagulation, agglomeration, and settling of the particles. Usually an addition of calcium sulfate is unnecessary, because it is present in the wastewater from the sand-flotation process. Generally, it has been shown [33] that the clear effluent from the phosphate mining and beneficiation operation is not deleterious to fish life, but the occurrence of a dam break may result in adverse effects [19]. 

Semenova, M.G., Belyakova, L.E., Dickinson, E., Eliot-Laize, C., Polikarpov, Yu.N. (2005). Caseinate interactions in solution and in emulsions effect of temperature, pH and calcium ions. In Dickinson, E. (Ed.). Food Colloids Interactions, Microstructure and Processing, Cambridge, UK Royal Society of Chemistry, pp. 209-217. 

Precipitation refers to dissolved species (such as As(V) oxyanions) in water or other liquids reacting with other dissolved species (such as Ca2+, Fe3+, or manganese cations) to form solid insoluble reaction products. Precipitation may result from evaporation, oxidation, reduction, changes in pH, or the mixing of chemicals into an aqueous solution. For example, As(V) oxyanions in acid mine drainage could flow into a nearby pond and react with Ca2+ to precipitate calcium arsenates. The resulting precipitates may settle out of the host liquid, remain suspended, or possibly form colloids. Like sorption, precipitation is an important process that affects the movement of arsenic in natural environments and in removing arsenic from contaminated water (Chapters 3 and 7). 

Synthesis of oil soluble micellar calcium thiophosphate was performed in a one-step process involving the reaction of calcium oxide, tetraphosphorus decasulfide and water in the presence of an alkylaryl sulfonic acid. This product could be defined as a calcium thiophosphate hard-core surrounded by a calcium alkylarylsulphonate shell in accordance with a reverse micelle type association in oil. Three micellar products with the same chemical nature core were prepared, each with different core/shell ratio of 0.44, 0.92 and 1.54. Better performances are expected with products of higher core/shell ratios. The antiwear performance of micellar calcium carbonates is directly linked to the size of the mineral CaC03 colloidal particles. At a concentration of 2 % micellar cores, no antiwear effect is observed whatever the micellar size. At an intermediate concentration of 4 % of micellar cores, the wear scar diameter is clearly dependent on the micellar size, slipping from 1.70 mm to 1.10 mm, then to 0.79 mm when the core diameter moves from 4.37 nm to 6.07 nm, then to 6.78 nm. Size dependence is increased at a concentration of 5 % in colloidal cores. This clearly confirms the size dependence of the micellar cores on their antiwear performance (Delfort et al.,... 

Switching from the very hydrophilic clays towards other inorganic nanoparticles, e.g., colloidal silica, leads, in the interplay with polymerization in miniemulsions, into a potential structural complexity, which covers the whole range from embedded particles (such as in the case of the calcium carbonate and carbon blacks) to surface bound inorganic layers (such as in the case of the clays). For basic research they are ideal systems to analyze complex structure formation processes in emulsions, since the original droplet shows a structure which is essentially established by molecular forces and local energy considerations, and which is ideally just solidified into a polymer structure. 

In standard fresh cheese manufacture most of the original milk calcium is lost in the concentration step (either centrifugal separation or UF) where the desired protein and dry matter level is achieved, because the colloidal calcium, at acid pH values, is ionic and therefore leaves the casein micelle into the serum. While in the separation process the whey proteins and the calcium are lost in the serum, the UF process retains the whey proteins and, therefore, achieves a higher yield, but the calcium is still lost into the UF permeate. Fresh cheeses therefore are relatively low in calcium content. Figure 19.29 compares the conventional fresh cheese process with a new process proposal that can retain most of the milk calcium in the product. 

---