Abstract
Finished leather waste is a kind of dangerous solid waste generated by tanneries. Therefore, the effective management of finished leather waste would promote the green and long-term development of the leather industry. In this paper, finished leather waste was selected as raw materials to obtain collagen protein hydrolysate (CPH) with high protein content and then the feasibility study of CPH on gypsum retardation was investigated through comparative analysis with commonly used gypsum retarders. CPH exhibited a satisfactory retarding performance comparable to citric acid (CA) and sodium hexametaphosphate (SHMP), and the retarding performance of CPH on gypsum was gradually enhanced with the dosage increased. Strength measurement and SEM observation indicated that CPH decreased the strength loss of gypsum due to the less impact on gypsum crystals compared with CA and SHMP. Like CA and SHMP, CHP not only featured an effective delay effect on the rise in hydration degree but also changed the hydration heat characteristics in gypsum hydration. The characterization of gypsum hydration product by FTIR and XRD suggested that CPH, CA and SHMP markedly delayed the conversion of gypsum hemihydrate to gypsum dihydrate. Ca2+ concentration determination and XPS analysis further demonstrated that the introduction of retarder altered the chemical environment around calcium element in the gypsum system to delay the participation of calcium ions in the hydration reaction, therefore exhibiting retarding performance. This study reveals a practical and sustainable route for the utilization of finished leather waste, but also provides new theoretical guidance for the development of gypsum additives with high-retarding performance.
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