Sparingly soluble salts, deposition

With sparingly soluble salts of lead, the compactness of the deposits may be strongly influenced by the concentration of the relevant anion. Very low concentrations frequently resulting in imperfect coatings. 

Under-deposit corrosion is a particular type of corrosion caused by differential aeration. If sparingly soluble salts, loosely adherent corrosion products, algal, or other fouling, is deposited on a metal surface, then these areas become depleted in oxygen. Unfouled or less fouled areas have a greater supply of oxygen and hence become cathodic to the fouled areas. Thus, the anodic under-deposit areas will corrode preferentially. 

Sulfuric acid and sodium hexametaphosphate (SHMP) are injected in the feedwater line upstream of the cartridge filters. The sulfuric acid is injected to adjust the feedwater pH to a level of between 4 and 6. The purpose of acid injection is twofold. The primary purpose is to mitigate the possibility of calcium carbonate deposition by conversion of bicarbonate to carbon dioxide. Coincidentally, the rejection performance of the thin film composite membrane is pH sensitive and the optimum performance is at the operating pH level. SHMP is added to the feedwater as a threshold inhibitor to inhibit the crystalline growth of sparingly soluble salts such as calcium sulfate. 

These different characteristics of temperature and solubility can have a pronounced effect on scaling depending on whether or not the saturated solution is being heated or cooled. Inverse solubility salts are likely to form a deposit if the saturated solution is being heated the reverse is true for normal solubility salts. Problems are likely only to be encountered for sparingly soluble salts where relatively small changes of temperature have a significant effect on solubility. 

In addition to clays, many other minerals were formed. Sparingly-soluble salts such as calcium and magnesium carbonates and colloidal silica, were precipitated from sea-water and deposited on the sea bed, forming limestone, magnesian limestone, and silica rocks. 

Where sparingly soluble salts such es calcium carbonate, calcium sulfate, and calcium oxalate are present, they are essentially contaminants that can form scale deposits. The supersaturation potential is caused by both concentration and temperature effects. The inverse solubility characteristic acts to fevor deposition on the heat transfer surface. The contaminant may also be produced by a corrosion effect. 

When a sparingly soluble salt is placed in water, both anions and cations leave the surface of the solid and dissolve. This process continues until the solution is saturated with respect to the salt at this point a dynamic equilibrium is established in which the same number of ions are deposited on the surface as leave it in a given time. Once saturation has been reached, there is no net gain or loss of the solid phase. Conversely if the solid salt is placed in an aqueous solution, which is supersaturated with respect to the solid, there will be a net deposition of ions on the surface of the solid until equilibrium is reached at the same solute concentration as before. This concentration will be constant for a given substance at a specified temperature. Furthermore, the product of the ionic concentrations will be constant at a value known as the solubility... 

Base V, CjgHj or 26O2N2. This substance is present in small quantity (about 1-5 per cent.) in crude aphylline hydrochloride and when the base is liberated into ether from this salt, the solution deposits Base V on standing. It is sparingly soluble in ether or light petroleum, readily in benzene or alcohol and crystallises from benzene-light petroleum in colourless tablets, m.p. 137° (dec.). 

Engel A process for making potassium carbonate from potassium chloride obtained from the salt deposits at Stassfurt, Germany. The basis of the process is the formation of the sparingly soluble double salt MgKH(C03)2-4H20 when carbon dioxide is passed into a suspension of magnesium carbonate in aqueous potassium chloride ... 

Dichloro-tetrammino-platinic Chloride, [Pt(NH8)4Cl2]Cl2, is prepared by passing chlorine gas through a solution of tetrammino-platinous chloride till the liquid begins to turn red. From the cold dilute solution the salt crystallises with one molecule of water of crystallisation, whilst from more concentrated solutions the anhydrous salt is deposited. It may also be obtained by the action of ammonia on tetraehloro-dianunino-platinum. It crystallises in pale yellow microscopic oetahedra, is sparingly soluble in water, and only half of the chlorine is precipitated as silver chloride when the aqueous solution is treated with a cold solution of silver nitrate. Sulphuric acid eliminates only two molecules of chlorine.1... 

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