Rationalization of salt-related processes in the leather industry as a tool for minimization of their environmental impact

Abstract

The main purpose of our contribution is reducing the existing environmental burden related to the worldwide use of sodium chloride for raw hide curing. The essential step is rationalization of the curing process itself, since it determines the amount of salt to deal with in the subsequent operations such as pre-soaking, soaking, after-soaking and desalting of animal fleshings during their complex processing into valuable products. Leather industry has been known as major producer of total dissolved solids (TDS), particularly sodium chloride. The salt often gets to water environment, or right to the soils resulting in arid conditions in the spilling areas, from where it can be again washed away to water sources. Despite intensive search for alternative methods, sodium chloride remains the most common way of raw hide curing worldwide. This method not only represents considerable environmental burden, but insufficient application of the theory of the related transport phenomena also has economic impacts, such as high consumption of the preservation agent, of water and electric power. Rationalization of the curing process brings considerable reduction in the time necessary for proper curing and thus reduction in the amount of salt which in subsequent soaking operation would get to tannery effluents. Understanding the related transport processes, particularly diffusion of sodium chloride into or from the hide inner volume, gives ground for their optimization and thus to reduction of their adverse environmental impact as well as minimization of the consumption of sodium chloride, water and energies. Our approach lies in application of theoretical tools of chemical engineering, namely indirect modeling based on quantitative relations from the theory of transport phenomena. This method is in particular cases supported by experimentally measured data, mainly estimation of the value of the effective diffusion coefficient of sodium chloride in animal fleshings and its application in calculation the minimal time necessary for proper curing of raw hides. The acquired knowledge is applied in newly emerging industrial field, complex processing of animal fleshings into valuable products such as quality biodiesel and gelatin. The fleshings contain considerable amount of preservation salt, therefore desalting represents the key operation in their processing and the quality of the resulting products is highly dependent on the precise performance of the desalting process. The essential step leading to the optimization was the determination of the time dependence of sodium chloride concentration (from the hide surface towards its internal volume), in other words, a nonstationary concentration field of sodium chloride in the hide during the curing process. Subsequently, the solution of the model allowed the calculation of the optimum time necessary for sufficient preservation. © 2014 Nova Science Publishers, Inc.