<p>Integrated steel plants often dispose of solid waste (slag) in landfills, causing pollution and environmental issues. In this study, Silico-Manganese slag from a Ferro alloy plant was used as a substitute mold material for silica sand, combined with bentonite and coal dust. Scanning Electron Microscope analysis showed that silica sand particles are sub-angular, and coal dust particles are irregular and fragmented. In contrast, bentonite and Silico-Manganese slag particles are spherical and angular, respectively. The weight percentage of slag in the sand mold varied from 0 to 85%, and the mechanical properties such as green compressive strength, shear strength, permeability, and hardness were examined. It was observed that the green compressive strength, shear strength, and hardness values of slag-blended silica sand molds initially increased and then decreased with higher slag content. In contrast, permeability decreased continuously with increasing slag. The sand mold containing 15% Silico-Manganese slag exhibited optimal values for green compressive strength (1.32&#xa0;kg/cm²), mold hardness number (84.66), shear strength (0.145&#xa0;kg/cm²), and permeability number (326). A lab-scale trial of A356 alloy casting using the 15% Si–Mn slag-blended silica sand mold demonstrated that the casting was free from defects and had a smooth surface.</p>