Abstract
M.Tech.
A study was undertaken to develop and test the process for the recovery of high purity
chromium oxide green from chromium waste. The process developed has a combination of
leaching, ion exchange, coagulation, chelation and calcination. Based on the research
findings, strong acid cation resin (Purolite 106) and weak acid cation exchange (Lewatit NCP
80) resins were selected for extraction of aluminium Ill ions and chromium Ill ions
respectively. The optimal conditions for extraction of chromium (Ill) with ion exchange resins
from chromium leachate solution were established taking into account the composition and
the parameters of the chromium solution, the resin manufacturer's defined operating
conditions and the empirical dependencies established in previous studies on model solutions
of chromium (Ill). The effects of pH, compositions and the temperature on the extraction of
chromium (Ill) were also examined. The yield of chromium (Ill) from tannery chromium
hydroxide solid was about 96-98% after 35 min of phase contact with the sulphuric acid
solution. Chromium hydroxide with Cr20 3 content of 88% was achieved by extracting
chromium (Ill) with weak acid cation resin. The ferric and calcium ions present in the treated
chromium hydroxide product were then removed by soaking the hydroxide cake in 0.1 to 0.2M
ethyldiaminetretraacetic (EDTA) acid solution. The final product, chromium oxide green, with
a Cr20 3 content of at least 95.14% achieved with the described process.