An improved method and apparatus for treating chromium containing leather scrap to recover chromium compounds and to produce a protein hydrolysate. The leather scrap is fed into an upstream mixing zone of a reaction vessel along with an alkali metal solution and the scrap and the solution are mixed by a plurality of kneading paddles carried by a rotating shaft. The mixture is then passed to a downstream hydrolyzing zone and conveyed through the hydrolyzing zone by a spiral flight. The mixture is heated by the injection of steam to thereby produce a hydrolyzed mixture comprising a protein hydrolysate containing suspended, insoluble particles of chromium compound. The hydrolysate is separated from the precipitated chromium compounds and can be recirculated to the reaction vessel while the chromium compounds can be recovered for use in the tanning process. The concentrated hydrolysate can be subjected to electrophoresis to increase the concentration of any desired amino acid in the hydrolysate.