عنوان مقاله [English]
Although the mill modeling techniques have increasingly improved in recent years, but the ball mill Bond Work Index has still been in broad usage in the design of industrial mills. The Bond ball mill grind ability test is performed in a standard laboratory mill, until a circulating load of 250% is obtained. This Work Index provides the initial indication of specific power consumption (kWh/t) required to grind any particular ore. However, this technique is time consuming and requires 7 to 10 grinding tests. In this research, first, a simplified method based on the kinetics of grinding in ball mill is reviewed. The results of studies show that the grinding process, in short time, follows first-order kinetics and therefore by conducting just two ball mill grinding tests, the work index can be determined. This method was employed on the feed samples of Se-Chahun ball mill. The differences between the standard Bond Work Index and the Work Index obtained by this method, was less than 6%. Then, the Work Index measurements were conducted indirectly, by means of impact and abrasion test methods, on the feed samples of Choghart Autogenous mill. Impact tests, using Drop Weight testing device, on different size fractions of the sample (-16+12.5, -22.4+19, -31.5+25, -45+37.5 and -63+53 mm) at different levels of specific energy, Ecs, (0.1, 0.15, 0.25, 0.75, 1, 2 and 2.5 kWh/t) and the relevant index (t10) was determined. The empirical equation, t10=A (1-exp (-b*Ecs)), proposed by Napier-Munn et al.(1996), were fitted to the experimental data and the coefficients A and b were determined, as 56.4 and 1.21 respectively. These parameters are indications of ore resistance to impact grinding forces. Finally, the abrasion test on a 3 kg sample of -55+38 mm Choghart iron ore, in a 300mm diameter tumbling mill with four 10mm lifter bars, was performed and the relevant ta(t10/10) value was determined as 0.61. The empirical relations between the impact and abrasion indices and the Bond Work Index, A*b = -3.5 WI+117andta = 19.7 WI -1.34, proposed by researchers in JKMRC (Australia), were evaluated. The results obtained by the indirect methods, using impact and abrasion tests, were reasonably close (differences around 3%) to the standard Bond Work Index. Therefore the proposed methods can be used as an alternative means to determine the Bond Work Index. By using these methods, Bond Work Index can be determined quickly, accurately and at relatively lower cost.