Recovery and Reuse of Chromium from Tannery Waste Chrome-liquor using Solar Evaporation Process

Abstract

Recovering and reusing chrome from chrome effluent is critical for improving the mass balance of the tanning process and implementing the zero liquid discharge concept in the tanning industry. Conventional chrome recovery methods require a large amount of chemicals or energy to recycle the chromium. Chrome recovery by solar evaporation has not been implemented yet in the tanning industry. It is mainly practised in seawater salt extraction. In this study, we demonstrate the construction of highly efficient solar evaporators, using photothermal materials. Our focus is on efficient solar-to-vapour conversion and chrome recovery. The average evaporation rate was calculated and found 38.69 mL/hour, which remained almost steady within 2.5 months of data collection. The highest temperature observed during the process was 108 °C and 62°C in the focal region and condenser respectively. After collecting the solid chromium, basicity was measured at 85.02%, and treated with sulphuric acid to achieve 33% basicity. Recovered chrome and fresh chrome at 0:8, 5:3, and 8:0 were used for chrome tanning and tested for various chemical and physical parameters of tanned leather. The shrinkage temperature of the produced leather was found to be more than 100 °C. Physical characteristics such as tensile strength and percentage of elongation test, stitch tear strength, ball bursting strength and flexing endurance showed better results than conventional methods. This new kind of research offers a promising solution that can reduce the environmental impact of the tanning industry while also providing a sustainable source of chromium for a low-cost strategy and high-performance evaporation approach.