Using ashes from incineration of chromium sulphate tanned leather scrap part 2: Tanning liquors, additives in footwear adhesives and fillers in mortars

Abstract

Chromium is the basis of leather manufacture and its extractable reserves are limited in distribution, mainly in South Africa, Zimbabwe and ex-USSR countries. Almost 20% of the metal is used by the chemical industry where one third of it goes into leather production as chromium sulphate tanning agent.(1) The European Union depends on chromium imports as for most other metals. After burning leather scrap tanned with chromium sulphate, the very rich chromium resulting ashes may contain chromium (VI) in such a concentration that it becomes a hazardous waste and needs careful handling.(2,3) Thus, both economic and environmental reasons suggest the use of these ashes. This paper follows another(4) in presenting some of the work carried out under CRAFT project BRST-CT96-5085, where leather incineration ashes generated by two different pilot-combustion systems, respectively a fixed grill incinerator (FGI) and a fluidized bed incinerator (FBI) were characterized and some alternatives for using those ashes were studied. In the previous paper two routes for recovering chromium from leather ashes were considered as well as the influence of some factors on their efficiency. Now, producing chromium sulphate tanning liquors with chromium leached from the ashes is considered, as well as some other alternatives of using those ashes, namely as additives in footwear adhesives and fillers in mortars.