Incorporation of chromium-tanned leather residue in mortars

Abstract

To protect the environment there is worldwide pressure to establish sustainable conditions for all kinds of industrial processes. In the leather industry, tanning is the main process used to protect the hide from environmental effects such as heat and microbial degradation. In Brazil, 60% of the leather that is processed comes from an area in the state of Rio Grande do Sul called Vale dos Sinos, which has approximately 90 tanneries and accounts for 30% of Brazilian leather exports. Studies show that 30% of the leather processed in tanneries is rejected, especially after the shaving process, in which many chemical products are used. Chromium-tanned leather has been used for many decades in the manufacturing of a large variety of leather products for personal use. This process generates liquid and solid waste containing chromium salts that are discharged as effluents into the environment, mainly in water and into the ground. Some solutions can be used to minimise the amount of chromium residue, such as the increase of material fixation due to the control of pH, the recycling of chrome tanning liquors to reduce the discharge into wastewater, the pyrolysis of material for the production of activated carbon and use in Portland cement clinker production. In order to contribute with another alternative for the disposal of this residue, the present study evaluated the incorporation of the residue into mortars. Three mortar mixture proportions were studied, each one with five levels of sand replacement by residue. Tests were conducted in order to verify the mortar properties, in the fresh and hardened state and the evaluation of total and chrome VI. The results showed that there is potential for using chromium-tanned leather residue in civil engineering and that technical, economic and environmental benefits can be obtained.