Gypsum Impurities

Phosphoric Acid 27 122-161 50-72 - - E E H2SO4 and gypsum impurities, aeration... 

Calcareous minerals such as gypsum [13397-24-5] when added in stoichiometric amounts relative to the barite impurities, reduce acid-soluble barium losses (16). 

Typical applications in the chemical field (Beaver, op. cit.) include detarring of manufactured gas, removal of acid mist and impurities in contact sulfuric acid plants, recovery of phosphoric acid mists, removal of dusts in gases from roasters, sintering machines, calciners, cement and lime Idlns, blast furnaces, carbon-black furnaces, regenerators on fluid-catalyst units, chemical-recoveiy furnaces in soda and sulfate pulp mills, and gypsum kettles. Figure 17-74 shows a vertical-flow steel-plate-type precipitator similar to a type used for catalyst-dust collection in certain fluid-catalyst plants. 

Guillini A process for making gypsum from the waste product from the Wet Process for making phosphoric acid. The waste is heated with water in an autoclave this removes impurities and converts the calcium sulfate dihydrate to the hemi-hydrate. 

The hydrochloric-acid solution is precipitated by ammonia, and the earthy phosphates filtered, dried, and weighed, Tho precipitate obtained by ammonia when added to the sand and gypsum, ought to be nearly the same as the weight of ash left by the wator, - When tlu s is not the case it is due to impurities, such as car- bonate of lime, and the loss of weight corresponds to the quantity of this substance present. 

Developments of recent years include plants designed to precipitate the calcium sulfate in the form of the hemihydrate instead of gypsum, hi special cases, hydrochloric acid is used instead of sulfuric acid for rock digestion, the phosphoric acid being recovered in quite pure form by solvent extraction. Solvent-extraction methods have also been developed for the purification of merchant-grade acid, which normally contains impurities amounting to 12 18% of the phosphoric acid content. Processes for recovering part of the fluorine in the phosphate rock are in commercial use. 

True English red should contain only small quantities of impurities (usually not more than 1-2% of substances insoluble in acids) and should consist essen tially of ferric oxide it should not contain copper or free sulphuric add. Products containing barium sulphate or chalk or gypsum in other than very small quantities are to be regarded as intentional mixtures as much as 80% of gypsum is found in some commercial samples. 

Minium may contain various impurities derived from the raw materials of its manufacture, e.g., calcium salts and oxides of iron and copper. It may be adulterated with day, chalk, gypsum, heavy spar, lead sulphate, brickdust, ochre and other colours with a basis of ferric oxide, and artificial organic dyes. 

Cinnabar and vermilion usually contain only small proportions of impurities from the prime materials vermilion may also contain impurities due to the method of preparation, namely, small quantities of metallic mercury, mercuric nitrate and free sulphur. These products are, however, often adulterated with ferric oxide, minium, chrome red, brickdust, gypsum, heavy spar, clay, ammonium chloride, dragon s blood, carmine and artificial organic dyes. Sometimes also arsenic and antimony sulphides are added to modify the colour. 

It may contain, as impurities or as additions, other cadmium compounds, zinc compounds and free sulphur, and it may also be adulterated with chrome yellow, cinnabar, arsenic sulphide, heavy spar and gypsum. 

They may contain as impurities, small quantities of alkali, sulphates and chlorides and are often adulterated with kaolin, heavy spar, gypsum, chalk, white lead, zinc white, magnesia, starch, etc. 

There is no current commercial biologic process for the production of succinic acid. In past laboratory systems, when succinic acid has been produced by fermentation, lime is added to the fermentation medium to neutralize the acid, yielding calcium succinate (2). The calcium succinate salt then precipitates out of the solution. Subsequently, sulfuric acid is added to the salt to produce the free soluble succinic acid and solid calcium sulfate (gypsum). The acid is then purified with several washings over a sorbent to remove impurities. The disposal of the solid waste is both a directly economic and an environmental concern, as is the cost of the raw materials. Some key process-related problems have been identified as follows (1) the separation of dilute product streams and the related costs of recovery, (2) the elimination of the salt waste from the current purification process, and (3) the reduction of inhibition to the product succinic acid on the fermentation itself. Acetic acid is also a byproduct of the fermentation of glucose by Anaerobiospirillium succiniciproducens almost 1 mol of acetate will be produced for every 2 mol of succinate (3). Under certain cultivation conditions by a mutant Escherichia coli, lesser amounts of acetate can be produced (4,5). This byproduct will also need to be separated. 

Phosphate rock contains about 3.5 percent fluorine, some of which is recovered as a byproduct in manufacturing wet process phosphoric acid. During acidulation, the fluorine is released as hydrofluoric acid, HF, which reacts with the silica present as an impurity in the rock to form fluosilicic acid, H2SiF6. Some of the fluorine is lost with the gypsum as sodium or potassium fluosilicates, and some remains dissolved in the filter acid. When the acid is concentrated, much of the fluorine in the feed is boiled off, appearing as HF and silicon tetrafluoride, SiF4, in the vapors. 

Areas of the earth that are rich in sulfur minerals also contain limestone, CaC03, and gypsum, CaS04. These impure ores may contain up to as much as 25% elemental sulfur. 

Syngenite, if present, decomposes at 250-300°C. Small amounts of CH can occur due to hydration, and of CaCOj due to carbonation during i milling or storage, impurity in the gypsum, or, where specification allows it, deliberate addition. The increasing tendency to allow additions of sub-1 stances other than calcium sulphate may lead to the presence of other phases ... 

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