Closed-loop Liming and Chrome Tanning Systems in Full-scale Wet Blue Manufacture

Abstract

Closed-loop liming/unhairing and chromium tanning systemsare now established for the full-scale manufacture of bovine wetblue leathers. The technology ensures full recovery and reuse ofthe concentrated used processing f loats, and four majortanneries are now producing some 72,000 hides per week as highquality wet blue leathers from salted American, European andAustralian wet salted hides. These are for their own use, sales,and contract tanningIn practice there are no discharges or washings for effluenttreatment from either the liming/unhairing or the acid/saltpickle and chromium tanning processes. Accordingly, there isno chemical wastage from these two major stages within leathermaking. There are significant saving in processing chemicals –lime, sodium sulfide/hydrosulfide, salt, acids, chromiumtanning agents and water too. The problems associated withtreating waste waters from these two environmentally difficultstages are thus totally avoided.Based on independent on-site surveys1 within each of these fourtanneries, this paper shows how the technology is managed inpractice. In particular it shows how the process stabilizes withinthese processing loops, and how a continuous increase in neutralsalts is avoided.