Precipitation from solutions with carbonate

Lateritic Ores. The process used at the Nicaro plant in Cuba requires that the dried ore be roasted in a reducing atmosphere of carbon monoxide at 760°C for 90 minutes. The reduced ore is cooled and discharged into an ammoniacal leaching solution. Nickel and cobalt are held in solution until the soflds are precipitated. The solution is then thickened, filtered, and steam heated to eliminate the ammonia. Nickel and cobalt are precipitated from solution as carbonates and sulfates. This method (8) has several disadvantages (/) a relatively high reduction temperature and a long reaction time (2) formation of nickel oxides (J) a low recovery of nickel and the contamination of nickel with cobalt and (4) low cobalt recovery. Modifications to this process have been proposed but all include the undesirable high 760°C reduction temperature (9). 

Chloro-pentammino-cobaltic Bromide, [Co(NH3)5Cl]Bra, may be prepared from the chloride by treating a solution, which has been made slightly acid with dilute sulphuric acid, with well-cooled hydro-bromic acid. The precipitate formed is washed with dilute aqueous hydrogen bromide and then with alcohol. It may be formed also from the corresponding chloro-carbonate by precipitating from solution with concentrated hydrobromic acid. It crystallises in red oetahedra, and is more easily soluble than the chloride. 

It may be prepared by mixing a solution of eobaltous nitrate with a mixture of ammonium carbonate and ammonia solution and allowing the liquid to stand for some time. Dark red crystals separate and are collected and recrystallised from hot water. In order to obtain the salt in a pure state it is transformed into the iodide by treating with hydr-iodie acid, the iodide precipitated from solution with alcohol, crystallised from water, and transformed into the nitrate by the addition of a concentrated solution of silver nitrate to an aqueous solution. The silver iodide is filtered oft and the nitrate separated from the filtrate by the addition of alcohol. The salt does not give the normal reactions for a carbonate and is unstable towards acids.2... 

Tl>e base is only slightly soluble in ether, thus rendering its use uneconomical. It may be extracted with chloroform and precipitated from the dried chloroform solution with carbon tetrachloride. 

Sodium bicarbonate precipitates from solution and is recovered by filtration. Ammonium chloride is then crystallised from the filtrate, separated, washed, and dried. The exact proportion of ammonium chloride recovered depends on the relative demands for sodium carbonate and ammonium chloride. If economic conditions requite, part of the ammonia can be recovered and returned to the hrine-ammoniation step by distillation of the ammonium chloride solution ia the presence of lime. The spent calcium chloride Hquor, a final product ia manufacture of sodium carbonate by the ammonia—soda process, can also be used to obtain ammonium chloride. This Hquor is treated with ammonia and carbon dioxide... 

Strontium carbonate also precipitates from strontium sulfide solution with carbon dioxide. Hydrogen sulfide is generated as a by-product of this reaction and reacts with sodium hydroxide to produce sodium hydrosulfide, which is sold as by-product. The abiUty of the black ash process to produce a product exceeding 95% strontium carbonate, from ores containing <85% strontium sulfate, has led to its predorninance. 

By far the most important ores of iron come from Precambrian banded iron formations (BIF), which are essentially chemical sediments of alternating siliceous and iron-rich bands. The most notable occurrences are those at Hamersley in Australia, Lake Superior in USA and Canada, Transvaal in South Africa, and Bihar and Karnataka in India. The important manganese deposits of the world are associated with sedimentary deposits the manganese nodules on the ocean floor are also chemically precipitated from solutions. Phosphorites, the main source of phosphates, are special types of sedimentary deposits formed under marine conditions. Bedded iron sulfide deposits are formed by sulfate reducing bacteria in sedimentary environments. Similarly uranium-vanadium in sandstone-type uranium deposits and stratiform lead and zinc concentrations associated with carbonate rocks owe their origin to syngenetic chemical precipitation. 

Carbonate Forms insoluble carbonates with cations under basic conditions Precipitates from solution... 

Polonium tetraiodide (8) is a black solid which sublimes in nitrogen at 200°C with partial decomposition to the metal. It is formed from the elements at 40°C/1 mm, by treating polonium dioxide or hydroxide with 0.1 N hydriodic acid, and is precipitated from solutions of polonium(lV) in dilute hydrochloric acid on the addition of 0.1 N hydriodic acid. It is also obtained as a black sublimate by heating polonium dioxide in hydrogen iodide at 200°C a black addition compound (PoCVxHI) is formed in the cold. Polonium metal does not react with iodine dissolved in carbon tetrachloride, but with iodine dissolved in benzene it does react to some extent. 

Sepiolite and palygorskite have a rather special composition and seem to be related to specific mineral parageneses. They appear to be stably associated with montmorillonite, corrensite, serpentine, chert, sulfates, carbonates and various salts. They are found in deposits typified by processes of chemical precipitation or solution-solid equilibria (Millot, 1964) and are therefore rarely associated in sediments with large quantities of detrital minerals. Their chemical environment of formation is in all evidence impoverished in alumina and divalent iron. Their frequent association with evaporites, carbonates and cherts indicate that they came from solutions with high chlorinity. 

The first commercially successfull synthetic nacreous pigments were hexagonal platelet crystals of lead salts Thiosulfate, hydrogen phosphate, hydrogen arsenate and most important nowadays, basic carbonate. Basic lead carbonate [1319-46-6] Pb(OH2) 2PbC03, Mr 775.7, is precipitated from aqueous lead acetate or lead propionate solutions with carbon dioxide ... 

Cyclobutanone is an important synthetic starting material (e.g. see Expt 5.41) recently a simple synthesis from readily available materials has been reported.6 The synthesis (Expt 7.13) involves the formation of l,3-bis[bromo-magnesio]propane and its further reaction with carbon dioxide to form the complex (36), which precipitates from solution thus simplifying the purification procedure. Although the overall yield is low (13%), this is compensated for by the cheapness of the reagents and the simplicity of the procedure. 

To a 12 L 3-neck round bottom flask was added isopropyl acetate (6.5 L). The solvent was cooled to 0°C in an ice-water bath and 3-amino-l-propanol (1.14 kg, 15.1 mol) was added in one portion. To this stirring solution, benzyl chloroformate (1.20 kg, 7.03 mol) was added dropwise over 2 hours while maintaining the internal temperature of the flask between 10-15°C. After the addition was complete, the reaction mixture was allowed to stir for an additional 0.3 hour after which time water (3.5 L) was added in one portion. The solution was then partitioned and washed with an additional 2 times 3.5 L of water. The organic layer was dried over potassium carbonate and concentrated to give a solid that was dissolved in excess isopropyl acetate and precipitated from solution by adding the compound to heptane. The solid was filtered under nitrogen to yield 1.20 kg (82%) of N-carbonylbenzyloxy-3-aminopropanol as a colorless solid. 

The high-temperature reduction of barium sulfate with coke yields the water-soluble barium sulfide (BaS), which is subsequently leached out. Treatment of barium sulfide with the relevant chemical yields the desired barium salt. Purification of the product is complicated by the impurities introduced in the coke. Pure barium carbonate and barium sulfate are made by precipitation from solutions of water-soluble barium salts. 

The benzimidazoles, as we have seen, are weak bases that are soluble in aqueous acids but may be precipitated from them by the addition of a stronger base such as ammonium hydroxide. The benzimidazoles are amphoteric substances, with acidic properties also, as shown by the formation of copper, silver, and other insoluble salts they are soluble in an excess of a strong base such as sodium hydroxide and may be precipitated from solution in that base by the addition of carbon dioxide. 

Sodium tetrathionate, Na2S408.—The tetrathionate is prepared from the thiosulphate either by the action of iodine (p. 124) or by oxidation with cupric chloride.15 It can be precipitated from solution by addition of alcohol. With sodium carbonate it yields sodium thiosulphate 16... 

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