Water-insoluble alkali aluminium silicate having coarse particle size - is used in degreasing and pre-tanning hides, neutralising leather and tanning pelts

Parent patent discloses the use of water-insol., esp. water-contg. alkali Al silicates having formula (Cat2/nO)x.Al2O3.(SiO2)y, (I) (where Cat is alkali metal-, esp. Na ion; x is 0.7-1.5; y is 0.8-6 esp. 1.3-4) and Ca bonding capacity 20-200 mg CaO/g anhydrous active substance, in leather mfr. According to present modification, (I) used have particle size >25 mu to 5 mm, pref. 25-100 mu, and esp. for tanning 0.1-5 mm. (I) can replace water-polluting auxiliaries used in degreasing and pre-tanning unhaired pickle hides and in tanning and neutralising pelts and leather, esp. in Cr tanning. Coarser particles are more easily removed from waste water by sedimentation of filtration. Slower acid bonding with coarser particles is advantageous in Cr tanning.