Sodium Hydroxide, with Lime, from Sulphide

At the same pH made by different pH modifiers, the different flotation response of one sulphide mineral may arise from its effect on the potential of this mineral electrode. The change of potential of mineral electrodes with time at pH= 12 modified by NaOH and Ca(OH)2 is measured and demonstrated in Fig. 10.5. It follows that a mineral electrode potential increases faster with the time at pH= 12 modified by sodium hydroxide and changes a little at the same pH modified by calcium hydroxide. When pH is adjusted by NaOH, the electrode potential of galena, sphalerite and p5oite increase rapidly, respectively, from -30, -12, and 70 mV at the initial stage to -10, 10, and 110 mV after 50 min. When pH is modified by lime, the electrode potential of galena, sphalerite and pyrite... 

The sulphate process consists in kiering pieces of wood in a solution composed of sodium hydroxide, sodium sulphide and sodium carbonate in a 65 15 20 ratio. The concentration of the solution is 10-12% of NaOH. Boiling at a temperature of 170-175°C under pressure lasts about 6 hr, of which 3 hr are required for heating, the other 3 hr being the kiering proper. Cellulose is then separated from the lye, washed with water, bleached, and subjected to final purification. The lye is condensed, evaporated to dryness, then sodium sulphate is added, and the whole is calcined. The sodium sulphate is thus reduced to sodium sulphide. Unchanged sulphate and the excess of carbonate are removed by addition of milk of lime. 

The alcohol is purified by shaking with aqueous potassium hydroxide and extracting with diethyl ether that has been freed from peroxides with silver nitrate and sodium hydroxide. After being washed, the extract is treated with saturated sodium hydrogen sulphide solution, filtered, washed and dried over potassium carbonate. After removal of the ether, the alcohol is distilled under reduced pressure and the middle fraction dried over lime that has been burned in an atmosphere of nitrogen. 

What became known as the Leblanc process was actually several interrelated processes. Salt was first reacted with sulphuric acid in a cast-iron pan, then in a reverberator furnace (in which heat was apphed from a flame blown from a separate chamber, not in direct contact with the salt), to produce saltcake (sodium sulphate), with hydrochloric acid released as a waste gas. Saltcake was used to make sodium carbonate, or roasted with limestone (calcium carbonate) and coal or coke to produce black ash. This mixture of sodium carbonate, calcium sulphide, sodium sulphide, hme, salt, carbon, and ash could be treated further with hot water to produce impure sodium carbonate in solution, evaporated into soda crystals (washing soda), or heated to yield anhydrous sodium carbonate. The latter, in turn, could be reacted with lime to made caustic soda (sodium hydroxide), the strongest commercial alkali then available. 

MacArthur s process is as follows —The ore is ground small enough to pass through 20-mesh, and is treated with a solution of sodium hydroxide of not more than 2 per cent, strength, at a temperature of 100° C. The filtered solution is precipitated by carbon dioxide obtained from a lime-kiln. The antimony precipitate obtained is in the form of a red amorphous sulphide, which is collected in a filter-press, while the filtrate, containing sodium carbonate, is causticised by lime from the kiln, ready for further use. The process is therefore continuous. 

After filtration, addition of sodium sulphide to the clear solution effects the precipitation of the three metals, cobalt, nickel, and manganese, as sulphides. Digestion with the calculated quantity of ferric chloride oxidises the manganese sulphide to sulphate, which passes into solution. The residue consists of cobalt and nickel sulphides, which are washed and converted into their soluble sulphates by roasting. The sulphates are extracted with water, and converted into chlorides by addition of calcium chloride solution. Their separation is effected g.s follows The requisite fraction of the chloride solution is precipitated with milk of lime, and the insoluble hydroxides of nickel and cobalt thus obtained are oxidised to the black hydroxides by treatment with chlorine. The. washed precipitate is then introduced into the remainder of the chloride solution, and the whole is well stirred and heated, when the black hydrated oxide of nickel passes, into solution, displacing tlm Remainder of. the cobalt from the solution, into. the precipitate.. The final product is thus a suspension of hydrated peroxide.of cobalt,in p. solution of nickel chloride, from which idle cobalt precipitate is removed by filtration, washed, and ignited, to the black oxide. 

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