GB565969A - Improvements in the de-tanning of chrome-tanned leather - Google Patents

Abstract

565,969. Detanning leather. LEINER, A. May 12, 1943, Nos. 7540 and 11154. [Class 76] In a process for de-tanning chrome-tanned leather by immersion in a weak alkaline solution followed by treatment with a weak acidic solution, a soluble inorganic salt is incorporated in the acid solution to reduce or prevent swelling of the leather material. The weak alkali may be a 2 per cent suspension of lime, or a solution of caustic soda or sodium carbonate, and may have included in it 5 per cent of bleaching powder or a small amount of hydrogen peroxide. Weak sulphuric or hydrochloric acid may be used for the acid treatment. Sodium chloride and sulphate are the preferred added salts, other examples being chlorides, sulphates, phosphates and acid phosphates of potassium and ammonium, chlorides of calcium and magnesium, sodium acid phosphate, acid sulphates of sodium and potassium, and ammonium, sodium, or potassium alums. From 1-7 per cent by weight of the salt may be used, the preferred amount in the case of sodium chloride or sulphate being 5 per cent. A solution of an acid salt, such as sodium bisulphate, may be used in place of the acid and salt solution. The acid and alkali treatments may be repeated to extract more chrome from the leather. Examples describe the treatment of chrome splits and chrome shavings, in the latter case the acid treatment being followed by washing with 5 per cent salt solution, then with a 3 per cent soda ash solution and finally with 1 per cent hydrochloric acid. The acid liquors and the 5 per cent salt solution washings may be treated with caustic soda solution and filtered to recover the chrome.