Kiln-fired clay bricks synergizing nickel–chromium plating sludge and fly ash: mechanical characteristics and cradle-to-gate life cycle assessment

Abstract

Life cycle assessment (LCA) of novel fired clay bricks with synergistic co-valorization of nickel-chrome plating sludge (NCPS) and fly ash (FA) is reported. 0%, 20%, and 37.5% FA was added to improve sludge-deteriorated mechanical properties. Sludge bricks (SBs) exhibited compressive strength of 11.03 MPa, 17% water absorption, nil efflorescence, and permissible heavy metals’ leaching, complying with standards as first-class bricks. LCA was performed with the ReCiPe-2016 method, utilizing the primary experimental data, government reports, and the Ecoinvent v3.8 database. LCA analysis revealed that compared to clay bricks, SBs caused 30%, 43%, and 51% lesser harm to ecosystem quality, human health, and resource categories in the endpoint assessment. Kiln emissions, coal, clay, and transportation were chief contributors, but their cumulative endpoint impacts significantly reduced (38%, 52%, 55%, and 45%) on switching to the SBs. Terrestrial acidification, global warming, photochemical oxidant formation, and particulate matter emissions significantly affected midpoint categories. However, their impacts got reduced by 52–57% with SBs. With global annual clay brick production exceeding 1.5 trillion, agricultural soil mining causes irreversible depletion of nitrogen, phosphorous, potassium, and organic carbon in the soil. SBs utilize only 50% clay, adding substantially to environmental savings. Successful NCPS immobilization in bricks prevents leaching hazards and avoids scientific landfill construction. With a calorific value of 945 kcal/kg, NCPS acts as internal fuel during firing, reducing the external coal requirement. This work establishes the techno-environmental feasibility of recycling NCPS and producing better-performing bricks with lower environmental impacts.