Understanding charge effects on marked ball wear rates – A corrosion study

To measure the wear rates of grinding balls within a ball mill, marked ball wear tests (MBWTs) have been used extensively. Using the wear rates from a MBWT, operators select the most cost-effective media for their grinding application. One factor that a MBWT does not account for is the possible interaction between different media materials which could affect their corrosion rates. Galvanic coupling between dissimilar metals can cause significant changes in their corrosion rates. While galvanic interactions between minerals and grinding media have been studied, the interaction between dissimilar media has not. Corrosion rates and potentials of modern high carbon steel (HCS) and high chromium white iron (HCWI) grinding balls were found using an electrochemical testing technique as a function of pH, chloride concentration, and dissolved oxygen content in a simulated mill water (electrolyte). The impact of the chromium content of the grinding media was also evaluated. Through experimental results and application of corrosion theory, galvanic coupling appears to be present between HCS and HCWI in most of the conditions examined. Galvanic coupling was determined to impact corrosion rates significantly. At a 1 to 10 HCWI to HCS surface area ratio (similar to a MBWT where HCWI is added to a HCS charge), HCWI’s coupled corrosion rate could decrease by 98% as compared to its uncoupled rate. From these results, operators are cautioned to consider the possibility of galvanic coupling when considering the results of MBWTs --Abstract, page iv