Process Mineralogical Assessment of the Grinding Products of the Per Geijer Iron Oxide-Apatite Deposits
Information obtained from comminution test work at the laboratory scale can be utilized to characterize ore types and predict their behavior during comminution at the industrial scale. Comminution tests with a laboratory-scale rod and ball mill of 13 predefined ore types from the Per Geijer iron oxide-apatite deposits were conducted. The grinding setup refers to the so-called Malmberget method used at LKAB, characterized by a subsequent circuit of rod and ball mill grinding. The highest P80 values were obtained by grinding only in the rod mill for 10 min (step A). Ball mill grinding for 25 min (step B) and 35 min (step C) gave a very narrow range of P80 values. Hematite-dominated ore types had significantly higher P80 values after the primary grinding step A compared to the other ore types. Generally, Fe content increased in finer particle size classes while CaO and P contents decreased. The influence of silicates or phosphates is dependent on the dominant iron oxide. Magnetite-dominated ore types are more likely to be affected in their comminution behavior by the presence of silicate minerals. In contrast, hematite-dominant ore types are instead influenced by the presence of apatite. The difference in the degree of liberation of magnetite and hematite between ore types depends on size fractions rather than the amount of gangue in the ore most likely caused by very fine intergrowth of both iron oxides. A consolidation from 13 to 8 ore types is favored, supporting possible future mining of the Per Geijer deposits.
