Variability of the Ball Mill Bond’s Standard Test in a Ta Ore Due to the Lack of Standardization

There is no doubt about the practical interest of Fred Bond’s methodology in the field of comminution, not only in tumbling mills design and operation but also in mineral raw materials grindability characterization. Increasing energy efficiency in comminution operations globally is considered a significant challenge involving several Sustainable Development Goals (SDGs). In particular, the Bond work index (wi) is considered a critical parameter at an industrial scale, provided that power consumption in comminution operations accounts for up to 40% of operational costs. Despite this, the variability of wi when performing the ball mill Bond’s standard test is not always understood enough. This study shows the results of a variability analysis (a 33 factorial design) performed to elucidate the influence on wi of several parameters obtained from the particle size distribution (PSD) in feed and product. Results showed a clear variability in the work and grindability indexes with some of the variables considered.

A Review of Alternative Procedures to the Bond Ball Mill Standard Grindability Test

Over the years, alternative procedures to the Bond grindability test have been proposed aiming to avoid the need for the standard mill or to reduce and simplify the grinding procedure. Some of them use the standard mill, while others are based on a non-standard mill or computation techniques. Therefore, papers targeting to propose a better alternative claim to improve validity, to reduce test duration, or to propose simpler and faster alternative methods for determining the Bond work index (wi). In this review paper, a compilation and critical analysis of selected proposals is performed, concluding that some of the short procedures could be useful for control purposes, while the simulation-based procedures could be interesting within a process digitalisation strategy.

Unveiling the Link between the Third Law of Comminution and the Grinding Kinetics Behaviour of Several Ores

As a continuation of a previous research work carried out to estimate the Bond work index (wi) by using a simulator based on the cumulative kinetic model (CKM), a deeper analysis was carried out to determine the link between the kinetic and energy parameters in the case of metalliferous and non-metallic ore samples. The results evidenced a relationship between the CKM kinetic parameter k and the grindability index gbp; and also with the wi, obtained following the standard procedure. An excellent correlation was obtained in both cases, posing the definition of alternative work index estimation tests with the advantages of more straightforward and quicker laboratory procedures.

Variability Study of Bond Work Index and Grindability Index on Various Critical Metal Ores

It is a well-known fact that the value of the Bond work index (wi) for a given ore varies along with the grinding size. In this study, a variability bysis is carried out with the Bond standard grindability tests on different critical metal ores (W, Ta), ranging from coarse grinding (rod mills) to fine grinding (ball mills). The relationship between wiand grinding size did not show a clear correlation, while the grindability index (gpr) and the grinding size showed a robust correlation, fitting in all cases to a quadratic curve with a very high regression coefficient. This result suggests that, when performing correlation studies among ore grindability and rock mechanics parameters, it is advised to use the grindability index instead of the Bond work index.

Beneficiation Studies of the Low-Grade Skarn Phosphate from Mactung Tungsten Deposit, Yukon, Canada

A preliminary beneficiation study of low-grade skarn phosphate rocks from Mactung tungsten deposit, along the Yukon and Northwest Territories border in Canada, was carried out through standard Bond Work Index, grinding test and laboratory batch flotation tests. The skarn phosphate sample assayed 12.65% P2O5 (about 30% apatite), 31.71% CaO and 35.46% SiO2. The main gangue minerals included calcite, quartz, calc-silicates, amphibole, feldspar, and pyrrhotite. The sample had a Bond Work Index of 19.04 kWh/t, belonging to a hard ore category. The beneficiation study of the skarn phosphate sample was carried out using “direct–reverse flotation” method. The direct flotation was carried out using sodium carbonate, sodium silicate solution (water glass) and sodium oleate. Sulfuric acid and phosphoric acid were used in the reverse flotation of the carbonate gangue. One phosphorous rougher flotation, one bulk cleaner flotation and one carbonate reverse flotation at ore grind size of 86% passing 53 µm led to a phosphate concentrate assaying 28.68% P2O5, 12.06% SiO2, 0.72% MgO and 46.98% CaO, at a P2O5 recovery of 70.9%.