Eco-friendly construction materials: immobilizing chromium in non-fired bricks

The leather industry generates substantial solid waste, with shaving and buffing dust comprising approximately 20% of total tannery residues. Improper disposal of this protein-rich chromium-containing waste leads to significant environmental pollution. The feasibility of incorporating leather shaving and buffing dust, combined with rice husk ash (RHA) and river sand, into non-fired bricks, aiming to convert waste into sustainable construction materials, was investigated. Bricks were fabricated by partially replacing clay (0-20 wt%) with a mixture of leather dust and RHA in varying proportions, with and without cement, and were cured for 7, 14, and 28 days. Comprehensive characterization, including FT-IR, XRD, WD-XRF, TGA/DTG, XPS, and leaching tests, was conducted to evaluate physicochemical, mechanical, and environmental performance. The presence of chromium predominantly in the stable trivalent state (Cr³⁺) and its effective encapsulation within the brick matrix was confirmed by XPS analysis. The optimal composition, containing 10% leather dust and RHA with Gazipur Clay and 15% cement, achieved a compressive strength of 20.03 MPa at 28 days, meeting ASTM and BDS standards. Chromium leaching remained well below permissible limits, indicating effective immobilization. A time-dependent increase in chromium leaching was observed (0.1562 ppm at 7 days to 0.40195 ppm at 28 days), reflecting a diffusion-controlled release, yet remained well below permissible limits, demonstrating effective immobilization. Circular economic principles are supported by this approach by transforming hazardous waste into value-added construction materials. The findings suggest significant potential for industrial-scale application of leather waste-based bricks, contributing to sustainable, cost-effective, and eco-friendly building material production.