Calcium precipitated

Brine Preparation. Sodium chloride solutions are occasionally available naturally but they are more often obtained by solution mining of salt deposits. Raw, near-saturated brines containing low concentrations of impurities such as magnesium and calcium salts, are purified to prevent scaling of processing equipment and contamination of the product. Some brines also contain significant amounts of sulfates (see Chemicals FROMBRINe). Brine is usually purified by a lime—soda treatment where the magnesium is precipitated with milk of lime (Ca(OH)2) and the calcium precipitated with soda ash. After separation from the precipitated impurities, the brine is sent to the ammonia absorbers. 

The reaction of magnesium noncarbonate hardness with lime and with soda ash is a two step reaction since reaction 6 produces a reasonably soluble calcium salt that must react with in order to cause calcium precipitation ... 

Where a softener has not been provided, a higher volume of sludge can be expected in the BW. Typically, the calcium precipitates either as insoluble carbonate scale or as phosphate sludge except where a chelant-based chemical treatment program is employed (which is unlikely in smaller boiler plants) or when an all-polymer program is employed. 

In this system there is a useful cooperative effect between aliuninium, fluoride and calcium, which has been demonstrated by the solution studies of Ellis Wilson (1987). In the absence of aluminium, calcium precipitates as the fluoride at all pHs. Aluminium has the effect of preventing the precipitation of calcium as fluoride, again because it forms strong soluble complexes with fluoride. 

In normal operations, there is little chance for spent acid to contact the completion fluid as the well will usually be produced after perforation, effecting the removal of completion fluid prior to acidization. The fact that a calcium precipitation reaction can occur should be recognized by those using TKPP solutions as a clear completion fluid in well operations. A KC1 spacer is recommended to avoid completion problems in formations having high calcium brines. 

Radenti et al. reported the corrosion rate of a typical potassium chloride fluid of 247 mils/year at 212°F. In contrast, they found by substituting potassium carbonate for potassium chloride, the corrosion rate was reduced to 3 mils/year t10 . Unfortunately, potassium carbonate is not optimum as a drilling fluid additive because it can produce massive amounts of calcium precipitation, may elevate the pH to undesirable levels, and in all cases reduces the calcium ion concentration to such a low level as to promote destabililzing cation exchange with clay minerals. 

Sodium sulfite is also used to absorb sulfur dioxide, producing a bisulfite that is converted back to sodium sulfite by the addition of a calcium precipitating agent. 

Capital and operating costs are low, offering a short payback in comparison to conventional methods of sulphate removal such as brine purge and barium or calcium precipitation. 

Calcium Storage in the Absence of Calcium Precipitating Anions... 

Calcium precipitation of whey proteins produces a hydrated coagulum. Schmidt et al. (1979) found hardness of whey protein gels to be greatest when 11.1 mM calcium chloride was added, de Rham and Chanton (1984) observed that calcium concentrations critical for precipitation of whey proteins were independant of the calcium-to-protein ratios. 

Endogenous pectin esterases play an important role in citrus processing they have therefore been studied intensively. They cause cloud loss in citrus juices, which is due to the calcium precipitation of enzymatically de-esterified pectin. This is desirable in the production of lemon and lime juices but undesirable in the production of orange juice. In orange juice concentrates strong calcium pectate gels may form which cannot be reconstituted... 

Now, also recall that Mq, (= fcMrcd mass of calcium from the noncarbonate hardness of calcium precipitated. As before, let this mass be measured in kilograms. Also, let [Ca lmgnot, in mg/L, be the concentration of calcium not precipitated. Thus,... 

Again, as in previous chapters, the best place to investigate for determining the modes of removal is the table of solubility products constants as shown in Table 14.1. A precipitation product that has the lowest K p means that the substance is the most insoluble. As shown in the table, the phosphate ion can be precipitated using a calcium precipitant producing either Ca5(P04)3(0H)(j) or Ca3(P04)2. Of these two precipitates, Ca5(P04)3(0H)(j) has the smaller K p of 10" thus, it will be used as the criterion for the precipitation of phosphates. Ca5(P03)3(OH)(j) is also called calcium hydroxy apatite. 

Sayer JA, Carr G, Simmons NL Nephrocalcinosis Molecular insights into calcium precipitation within the kidney. Clinical Science 2004 106 549-561. 

In the Dow Chemical process calcium hydroxide is added to seawater, the precipitated hydroxide then being reacted with hydrogen chloride (the calcium precipitating as calcium sulfate due to the simultaneous addition of sulfuric acid) and the magnesium chloride solution is evaporated to dryness at ca. 200°C to produce a product with ca. 1.5 to 2 molecules of water. 

The solution used is 0.5 M NaHC03. It is adjusted to pH 8.5 with NaOH and contains 2.5 mg polyacrylamide per litre. The hydrogen carbonate ion displaces adsorbed phosphate from soil surfaces and also may aid the dissolution of calcium phosphates by maintaining the calcium concentration in solution at a low level because dissolving calcium precipitates as calcium carbonate. 

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