Grinding and grading is the preparation process after the crushing process, further grinding the ore in terms of particle size to make it conform to the processing required by the sorting operation. Quality of work grinding and classification work has a decisive influence on the beneficiation plant of economic and technical indicators, so each processing plant paid great attention to the grinding and classification operations.
(1) Measurement of ore
Ore concentrator comprises a number of metering ore, ore grade (with the amount of gold) and water content.
1. The amount of ore (generally referred to as dry ore)
The large-scale mine selection plant is equipped with various metering devices in front of the grinding machine, which can automatically record the amount of ore. The small-scale mine selection plant can use the scraper sampling and weighing method to record the ore. The amount of minerals recorded before the mill is called the accumulated amount of minerals, and it must be handled by a person. Every half month to one month, check with the total amount of mines in the crushing process, the two should be flat, otherwise the cause should be found and dealt with in time.
The metering device of the grinding machine shall be maintained by a special person, and at least once a month, the physical quantity shall be checked once, and the accumulated ore amount shall be corrected according to the result of the verification.
The ore supply of each grinding machine should be recorded regularly (automatic device reads once every hour, scraper weighing method once every half hour), in order to adjust the amount of ore in time, so that the grinding machine is in a balanced working state.
2. Ore moisture content
The ore belt is regularly sampled by a grinding machine, and the weight before and after drying is weighed, and the moisture content of the ore is calculated and recorded.
3. The grade of the original mine
Special personnel will intercept the ore flow in the overflow of the grading operation, take it once every hour, take eight samples per shift, and then send it to the laboratory to analyze the grades of gold, silver and other metals, as the original technical indicators of each sorting operation. data.
(2) Concentration of pulp
The slurry produced by the grinding and grading operation needs to have a certain concentration and fineness of grinding.
Pulp concentration
The slurry concentration is generally determined by the sorting method of the sorting operation. Workers in the ore dressing class must record the concentration of the slurry every half hour, and the concentration fluctuation range should not exceed ± 2% of the process requirements. If the fluctuation range is large, the amount of water supplied to the front and rear of the grinding machine and the amount of raw ore should be adjusted in time.
2. The fineness of the pulp
The fineness of the slurry refers to the fineness of the ore in the slurry, which is related to the size and shape of the crystal grain size of the mineral. The appropriate grinding fineness of each concentrator is determined by a mineral selectivity test, which is a sign of the degree of mineral monomer separation. The fineness of the slurry is expressed as a percentage of -200 mesh. During the production process of the plant, the fluctuation range of the fineness of the slurry shall not exceed ±2% of the process requirements. The fineness of the slurry should be measured periodically by rapid screening and recorded. Slurry fineness can also be controlled indirectly by controlling the overflow concentration.
(3) Grinding medium
The grinding medium is an object that grinds the ore particles, and its characteristics include density, loading amount (or filling coefficient), ratio, amount of addition, and wear characteristics.
1. The grinding medium of the ball mill is a metal sphere
The factory must calibrate the ball of different ball diameters and materials, and use large-density metal balls as much as possible to improve the grinding efficiency.
2. The ball load of the ball mill
The total amount of balls loaded into the ball is called the initial load. It should be calculated at 45% of the ball mill's effective volume (ie, the fill rate is 45%). During the whole production period, the ball mill should strive to keep the media filling rate between 42 and 45%, which is often achieved by regularly adding new balls.
The working revolution of the ball mill is often measured to stabilize it within the 85% critical number of revolutions. Otherwise, the ball loading amount (ie the filling factor) should be adjusted in time.
3. Matching ratio of the ball
The weight of the ball of various diameters as a percentage of the total load is called the ball ratio (particle size characteristics of the ball). The ball ratio must be calculated based on the particle size composition of the ball mill total feed (including sand return and new feed). Sometimes it can be selected by empirical data. For small ball mills, 120mm and 100mm balls can be replaced with 100mm or 80mm balls.
4. Check and determine the ball replacement system
In order to maintain the specified grinding efficiency, it is necessary to try to make the weight and ratio of the medium in the ball mill cylinder close to the weight and ratio of the initial loading. This requires mastering the ball filling system (weight and ratio).
(1) Clean the ball in the ball mill cylinder every quarter (or half a year). Accurately measure and record the total weight of the ball and the ratio of various ball spheres (discharge the ball).
(2) According to the record of the grinding concentration and the grinding efficiency during the clearing ball, the most suitable ball loading and ratio of the ball machine are determined.
(3) The ball filling record during the clearing period with the best grinding effect is also established to establish the best ball filling amount and ratio. Usually only one or two large balls are added, and each shift is added once in proportion.
(4) Post workers must make regular and quantitative ball replacement according to the process requirements.
(4) Operation and maintenance
1. Always check the motor, transmission components and bearings and temperature to maintain a temperature difference of 40-60 °C.
2. Keep the lubrication in good condition.
3. Regularly inspect the wear of the sprinklers of the ore mixer, and whether the bolts of the ball mill cylinder are fixed to leak the slurry.
4. Prepare wearing parts such as liners and metal balls. Replace the patch regularly as planned. When replacing the patch and discharging the ball, the discarded liner and the ball must be carefully cleaned to avoid loss of granular gold.
5. The post operator should try to maintain the balanced stability of the ball mill feeding amount, the amount of water before and after, and the amount of sand returned by the grading equipment ; The shifter should create good production conditions for succession.
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