STUDY OF LINER WEAR AND ITS CORRELATION TO MOVEMENT OF GRINDING BALL AND SIZE DISTRIBUTION OF SAG MILL PRODUCT AT PT AMMAN MINERAL NUSA TENGGARA

• Main Author: ANDI SETIANEGARA (NIM : 12514035), MOHAMMAD
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/29007
• Institution: Institut Teknologi Bandung

PT Amman Mineral Nusa Tenggara (PT AMNT) is a mining company that processes copper from ore to concentrate. PT AMNT has a processing capacity of around 120.000 tons of ore per day. PT AMNT uses two semi-autogenous (SAG) mills to grind the ore to have a suitable size in the subsequent process. Grinding is directed to occur under optimum condition. The optimum condition of grinding occurs when the grinding ball hits the ore instead of the liner. The grinding ball movement is influenced by one of SAG mill part called liner. The liner used in PT AMNT has a Hi-Lo configuration. The liner is installed around the inside of the SAG mill on the feed end (FE) and discharge end (DE). Each section consists of 72 row of liners with 36 high parts and 36 low parts mounted side by side. <br /> <br /> Along with its use, the liner will experience wear. Wear causes dimensional changes on the liner. Changes in dimensions will cause changes in the motion of the grinding ball so that the grinding performance changes. PT AMNT controls grinding performance by adjusting operating parameters, which is rotational speed and mill filling. The rotational speed is fixed at 10 rpm, while the mill filling can be set to a maximum value of 34%. In addition, the failure in SAG mill liner in PT AMNT is still frequent. The failure will certainly cause losses. Thus, research is needed on the liner wear and its effect on the grinding ball movement. In addition, it is also important to know the effect of mill filling on the size distribution of SAG mill product. <br /> <br /> A series of experiments have been carried out in this study. The liner profile was measured at each shutdown so that there was some liner profile data from the new liner until the liner worn-out and was removed. The liner profile was measured using a device called mechanical liner profile gauge. Measurements were made at three measurement point on each type of liner namely FE low, FE high, DE low and DE high. This profile data was correlated with the cumulative throughput of SAG mill in PT AMNT so that it could be known the wear rate and dimensional changes of the liner. Then, this profile data was used as input to the MillTraj software to simulate the movement of the grinding ball. Furthermore, for the same liner profile data, grinding ball movement was also simulated on several rotational speed. Then, samples were taken on the product of the SAG mill. Sampling were carried out at several variations of mill filling at three different sampling times on undersize and oversize of dewatering screen. The samples were then sieve-analyzed in sizes 6,75-75 mm for oversize samples and 38-12500 microns for undersize samples. <br /> <br /> v <br /> <br /> The results of data processing showed that the change in liner dimension due toe the increase in cumulative throughput was not uniform in all parts. Liner dimension changes were directly proportional to wear rate. The higher the dimensions of a liner section, the higher the wear rate. The highest wear rate occurred at the lifter high in FE and DE liner with 14,99 mm/million tons and 19,48 mm/million tons. Then, the more middle the position of the liner section in SAG mill, the higher the wear rate. The wear rate on the liner section at the middle of SAG mill was 3,2; 13,55; and 16,6 mm/million tons for the plate, lifter low and lifter high of FE liner and 2,47; 14,06; and 14,67 mm/million tons for the plate, lifter low, and lifter high of DE liner. <br /> <br /> Furthermore, changes in liner dimensions affect the grinding ball movement. That liner dimension was the angle and the height of the lifter of the liner. The smaller the lifter angle and the lifter height, the lower the impact point of the grinding ball. Lifter height had a significant effect on the grinding ball movement when the height of the lifter was lower than the diameter of the grinding ball. In such conditions, the lifter was unable to lift the grinding ball so that the grinding ball would tend to roll. The simulation results showed that the grinding ball movement was too high where at more than five million tons of cumulative throughput, the grinding ball started to not hit the liner. In addition, from the simulation at several rotational speeds, it was obtained the value of rotational speed in the range of lifespan of the use of the liner where the grinding ball movement was at optimum conditions. <br /> <br /> Then, the results of the product sieve analysis showed that the greater the value of the mill filling in SAG mill operations, the greater the P80 undersize, while the P80 oversize would be smaller. Thus, the greater the value of the mill filling, the size distribution would be wider and the product size would be coarser. This was due to a greater mill filling, toe would get closer to the impact point so that the grinding would be occured under impact mechanism. In contrast to small mill filling, the product size distribution became narrow and the product size was fines. This was due toe the occurance of grinding through abrasion mechanism.