Aluminium-alkali treatment

Alkali can be also recovered from waste alkali solution by diffusion dialysis using a cation exchange membrane.170 Table 6.8 shows example material balances of caustic soda recovery from waste alkali containing aluminum hydroxide and caustic soda (waste alkali from aluminium surface treatment).61 The recovery rate and purity of recovered caustic soda are changeable by selecting the membrane species and operation conditions. 

The chromate sealing treatment imparts to the anodic film a distinct yellow to brown colour, which is probably due to a basic aluminium chromate or alkali chromate adsorbed on to aluminium hydroxide. The film gives appreciable protection against marine exposure. 

In 1862, E. C. C. Stanford proposed the carbonization of the drift-weed in closed retorts so as to recover tar and ammoniacal liquor in suitable condensers. This modification did not flourish because of the subsequent difficulties in extracting soluble iodides from the charcoal. V. Vincent (1916) claims that soln. containing aluminium sulphate extract the alkali iodides from seaweed leaving behind the organic matter which prevents the direct precipitation of iodine or iodides. The alkali iodide soln. is treated with copper sulphate for cuprous iodide, or by soln. of sulphites for iodine. M. Paraf and J. A. Wanklyn proposed to heat the drift-weed first with alkali hydroxide so as to form oxalic and acetic acids, which could be crystallized from the lixivium. The economical treatment of seaweed for iodine has been discussed by A. Puge. 

Aldehydes and ketones may be reduced to the corresponding primary and secondary alcohols by reagents such as lithium aluminium hydride, sodium borohydride, sodium and ethanol or hydrogen over a platinum catalyst. A ketone is reduced to a methylene group under more vigorous conditions with zinc amalgam and concentrated hydrochloric acid (the Clemmensen reduction) or treatment of the hydrazone with alkali (the Wolff-Kishner reduction)) (Scheme 3.39). 

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