Preparation Of Spent Chrome Liquor For Reuse As Retaining Agent For Vegetable Tanned Leather

Abstract

Full vegetable tanned upper leathers were produced according to standard procedures with shrinkage temperature of 72°C. They were cleared with 0.5% oxalic acid to pH 3.0 and re-tanned with spent chrome liquor adjusted to pH of 2.0, 2.5 and 3.0 respectively with 40% NaOH solution. The initial chrome oxide content of the wastewater was determined before and after each process. Three (3) pieces of samples vegetable tanned leather measuring 7cm by 5cm were placed in 500 ml conical flask containing 400 ml of the conditioned spent chrome liquor and mechanically shaken continuously for4hours. After every batch, 1.0 ml of the reused spent chrome liquor and one (1) leather sample was withdrawn for chromium oxidecontent determination. The process was repeated three times, for each batch of spent liquor. The Chromium content of each retanned leather sample and the corresponding reused spent chrome liquor were determined using Atomic Absorption Spectroscopy. The Uv-spectroscopic method was also used to determine the exhaustion of the chromium from the used liquor to 78%. Results show a general reduction of Chromium content of the conditioned spent chrome liquor while it was increasing in the semi-chrome leather samples. The sample leathers produced from the conditioned spent chrome liquor after piling for four days gave an average of 1.6% Cr2O3 content and shrinkage temperatures of (TS) 79OC, 81OC, and 82OC below the CTL having 102OC. Other results indicate the reduction of chrome oxide content of the liquor which should have been discharged to the environment.