FIELD: leather industry. SUBSTANCE: leather waste is consecutively treated by alkali-salt and acid-salt solutions, in two stages for each. In the first stage of alkali-salt treatment, working solution is prepared by adding sulfuric acid to sodium hydroxide solution. Acid-salt treatment in its first stage involves solution containing sulfuric acid and sodium sulfate formed by mixing part of exhausted alkali-salt solution with sulfuric acid solution or with preliminarily corrected exhausted solution of the second stage of previous acid-salt treatment. In the second stage of alkali-salt treatment, preliminarily corrected exhausted solution from the first stage of alkali-salt treatment. EFFECT: simplified and reduced process, increased yield of collagen, and reduced power consumption. 1 tbl, 2 ex
