Chromium Conservation in Leather Tanning

摘要

Chromium recovery from wet-blue offal trimmings and shavings can be done with substantial chemical cost gains by incineration at 600C for 5 hours. Pretreating the offal with 0.5 Na2CO3 and air-drying prior to incineration produce CrO4(-2). By simply incinerating the offal, without pretreatment, an ash containing water insoluable Cr2O3 was produced. The CrO3 in the ash was purified by leaching with water. Chromium and crude protein were efficiently extracted from offal using 5 pct NaIO3, 5 pct H2SO4, and 3 pct NaCl at 40C. This procedure was effective but expensive. Satisfactory leather as to odor, appearance, and shrinkage temperature was made from chromium recovered from wet-blue offal by incineration and by extraction. Chromium conservation is possible by recycling chromium liquors and by precipitating chromium from spent tanning liquors prior to combining the liquors with other tannery wastes. Combining chromium liquors with other wastes introduces contaminants that make chromium recovery and reuse difficult. Leaching sludges with H2SO4 produced marginal chemical cost gains. Leather tanned with these solutions had satisfactory shrinkage temperature but the sludge odors and iron contamination were objectionable.