Abstract
The paper analyses the properties (chemical and mineral composition, microstructure, density, etc.) of recycled tannery sludge (TS) and the possibilities for using it in cement mortar mixture. Mortar specimens containing 3–12% of tannery sludge by weight of cement and 3–9% of tannery sludge by weight of sand were tested. Flowability, density, ultrasonic pulse velocity (UPV), flexural and compressive strength, water absorption and sorptivity of the mortar were analysed. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis of tannery sludge and mortar are presented. The tests revealed that replacement of 6% of cement with tannery sludge in the mix increased flexural and compressive strength and UPV values, whereas water absorption decreased. SEM and XRD analysis revealed that specimens with tannery sludge contained lower amounts of ettringite and higher amounts of portlandite; the obtained structure was denser and contained more calcium hydrosilicates (C-S-H). Chromium leaching values in cement mortars were found not to exceed the limit values set forth in Directive 2003/33/EC.
Highlights
Rational use of industrial waste is a major challenge in implementing the provisions of the Circular Economy Documentation and realising the concept of Cleaner Production when it comes to increasing production efficiency and reducing the risk to humans and the environment
The purpose of our work is to investigate the properties of dried tannery sludge (TS) waste and to determine its effect on the performance of cement mortars
This effect can be explained by a higher content of TS in the mix compared to the replacement of the part of the cement
Summary
Rational use of industrial waste is a major challenge in implementing the provisions of the Circular Economy Documentation and realising the concept of Cleaner Production when it comes to increasing production efficiency and reducing the risk to humans and the environment. Rational recycling of industrial waste is becoming a major challenge. The sludge from leather processing consists of organic and inorganic substances. The chemical composition of inorganic substances commonly presented in tannery sludge includes the following elements and their chemical compounds: nitrogen, ammonia, sulphides, calcium compounds, chromium (III) salts (especially sulphates) as well as high chromium content [1,2,3,4,5,6,7]. According to the current legislation [8,9], the permissible level of chromium in tannery sludge is 3 mg/kg
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