The verification of the desired capacity increase in the grinding circuits is performed by simulation studies as they suggest accurate and fast alternatives compared to expensive and labor-intensive methods, particularly for the evaluation of situations that require investment. In this study, simulation was used to evaluate the alternatives that can be made to increase the capacity from 38.86 tph to 90 tph in a grinding circuit where copper slag is autogenously milled. The slag sample was characterized by drop weight and abrasion tests to describe the breakage in autogenous (AG) milling. The performances of the existing circuit and equipment were determined by a comprehensive sampling study, and modeling studies were carried out to form the basis of the simulations. Simulation scenarios were evaluated as investment free and investment requiring alternatives. In the investment free option changing fresh feed size distribution was examined however, capacity could be increased up to only 42 tph. In investment option, increasing the mill motor capacities was simulated and 90 tph target throughput was provided. This result was validated in the plant by replacement of mill motors of AG and pebble mill for 1000 kW and 750 kW, respectively.