No abstract

In comminution, mill power plays a major role from the economics standpoint and is a critical design criterion. It is influenced by a range of parameters such as media charge level (ball filling), slurry filling, slurry concentration and mill speed. In this work, the effects of these operating parameters were investigated using a pilot mill (1000 × 500 mm). To this end, a copper ore (−1000 µm) was used to prepare the slurry. The tests covered a range of slurry filling (U) from 0 to 1.7 with media charge between 12% and 36% of the mill volume and six different speeds between 60% and 85% of critical speed. A power analyser was utilized to measure mill power. Increase in mill speed and ball filling leads to a remarkable increase in the amount of the power. Preliminary results show that there is a definite trend between the power and the slurry filling U. Mill power draw is maximum at slurry concentration 60–70% and slurry filling 0.84. An empirical equation was given that fits the data reasonably well.

To assess the effects of the mill operating parameters such as mill speed, ball filling, slurry concentration and slurry filling on grinding process and size distribution of mill product, it was endeavored to build a pilot model with smaller size than the mill. For this aim, a pilot mill with 1m × 0.5m was implemented. There are 15 lifters with 50mm height and face angle of 30˚. In the present work, the combination of the balls (40% of the balls with 60mm diameter, 40% of the balls with 40mm diameter and 20% of the balls with 25mm diameter) was used as grinding media with 10%, 15%, 20% and 25% of the total volume of the mill. The experiments were carried out at 60%, 70%, 80% and 90% of the critical speed. The feed of the mill is copper ore with the size smaller than 25.4 mm, which d80 and d50 of them are 12.7 and 8 mm, respectively and slurries with 40%, 50%, 60%, 70% and 80% of solid and the slurry filling between 0.5 and 2.5. The results showed that the best grinding and grading occurs at 70-80% of the critical speed and ball filling of 20-25%. Optimized grinding was observed when the slurry volume is 1-1.5 times of the ball bed voidage volume and the slurry concentration is between 60% and 70%. The mill grinding mechanism in this work is a combination of both impact and abrasion mechanisms.

The present paper aims to investigate the key points of kinematic of contents inside the mill (load orientation), namely the shoulder, toe, impact, and pool angles. The kinematic of the mill contents in wet grinding is influenced by a range of parameters such as: media charge level (ball filling), slurry filling, and mill speed. In this work the influence of these operating parameters was investigated using a pilot mill (1000 × 500 mm). To this end, a Copper ore (-1000 μm) was used to prepare slurry at 50% solids concentration by mass. The tests covered a range of slurry filling (U) from 0 to 2.92 with ball filling 24% and 30% of mill volume and 6 different speeds between 60% and 85% of critical speed. It is observed as the mill speed increases, the more the impact angle will decrease. Toe angle increases in the range 15-25 degrees by formation of the pool in mill and exertion of the floating (buoyancy) forces to the particles inside the mill. The more the mill speed and the slurry filling increase, the more the shoulder angle will increase. The increase in slurry volume leads to the elevation of the pool level and therefore, the pool angle will exponentially decrease.

To assess the effects of the mill operating parameters such as mill speed, ball filling, slurry concentration and slurry filling on grinding process and size distribution of mill product, it was endeavored to build a pilot model with smaller size than the mill. For this aim, a pilot mill with 1 m × 0.5 m was implemented. There are 15 lifters with 50 mm height and face angle of 30˚. In the present work, the combination of the balls (40% of the balls with 60 mm diameter, 40% of the balls with 40 mm diameter and 20% of the balls with 25 mm diameter) was used as grinding media with 10%, 15%, 20% and 25% of the total volume of the mill. The experiments were carried out at 60%, 70%, 80% and 90% of the critical speed. The feed of the mill is copper ore with the size smaller than 25.4 mm, which d80 and d50 of them are 12.7 and 8 mm, respectively and slurries with 40%, 50%, 60%, 70% and 80% of solid and the slurry filling between 0.5 and 2.5. The results showed that the best grinding and grading occurs at 70–80% of the critical speed and ball filling of 20–25%. Optimized grinding was observed when the slurry volume is 1–1.5 times of the ball bed voidage volume and the slurry concentration is between 60% and 70%. The mill grinding mechanism in this work is a combination of both impact and abrasion mechanisms.