Optimization of Ball Milling Parameters for Efficient Copper Slag Valorization

The ball milling process increasingly employed in a symbiotic materials recovery context is associated with high environmental footprint due to its energy-intensive nature. The current paper addresses this issue by optimizing the milling of copper slag, recognized as a promising alternative resource within the construction sector. The slag was milled in a stirred mill using stainless-steel (SS), carbon-steel, and yttria-stabilized zirconia (YSZ) balls with(out) grinding aid (GA). The milling time and energy, besides milled slag properties, were monitored. Performance variations of different milling balls were explained through the impact theory. Results show that efficient size reduction happens in the first hours regardless of the ball material and diameter. In a specific surface area (SSA) between 3600-3800cm2/g (d50=11µm), substituting SS with YSZ balls decreased milling time and energy by ∼50%, comparable to processes performed with GA. The addition of smaller balls (Ø6.3mm) to bigger balls (Ø9.5mm) caused energy consumption to decrease starting from SSA=3200±100cm2/g and cumulative particle size to slightly reduce. The effect of the ball-to-slag ratio on the milling efficiency was found stronger than the ball diameter change. A strong influence of the parameter optimization on the ball milling efficiency was proposed, potentially benefiting powder production industries.