The role of grinding media and water composition on the chemical characteristics in a laboratory ball mill

Milling processes have been predominantly studied in relation to their primary function of particle size reduction and liberation, with little attention paid to the underlying chemical changes induced by this process. Furthermore, most studies have been conducted in the presence of ore, making it difficult to establish a clear reference point for understanding the different effects of the milling conditions on the slurry chemistry as opposed to those imparted by the ore on the chemical environment. In this study, the effects of milling in the absence of ore have been investigated, considering variables such as process water and grinding media composition at different pH conditions. The effect of using a stainless-steel mill shell was also investigated using inert ceramic grinding media. It has been shown that the type of Fe ion present affects the mixed potential (Eh) and pH of the system. This, in turn, significantly impacts the availability of a collector such as SIBX in the slurry phase. Furthermore, the presence of ions in the process water, typical of those produced during recycling, was found to buffer pH and Eh changes when Fe(III) is the dominant Fe species. Compared to milling under natural conditions, pH control could reduce the effects of both media and water type on Eh. The relative amount of dissolved Fe present correlated the most with the observed Eh trends when milling with different media types at natural pH. Dissolution of Fe attributable to the mill shell was also observed when using ceramic media. Therefore, the composition of the mill shell may have a significant impact on the reactions occurring in the slurry phase. It is proposed that the results of this investigation may lead to a better understanding of the relative effects of grinding media, ore type, and the nature of the mill shell on the slurry chemistry and, thus, on the ultimate downstream processes such as flotation.