Investment in ore selection in Angang Dagushan and other mineral processing plants (1)

Ore beneficiation benefits ironmaking, but the ore concentrator has to pay a price. The investment in ore beneficiation is mainly reflected in increasing investment in infrastructure and technical transformation of the ore concentrator. It also affects other indicators such as recovery rate and processing capacity, thereby reducing concentrate output and increasing concentrate costs. (1) Increase investment in mineral processing Ore selection must take certain technical transformation measures and increase grinding and processing equipment, thus increasing infrastructure costs. The magnetic separation workshop of Ansteel Dagushan Mineral Concentrator has 15 ф2.7×2.1m ball mill series, with a designed annual raw ore processing capacity of 3.6 million tons. When produced according to the original design process from 1972 to 1976, the concentrate grade has been fluctuating between 62.78 and 62.78. Between 63.71%. In order to improve the concentrate grade, the plant changed the original design process to a fine screen self-circulation process in 1977. While the metal recovery rate and ball mill capacity remained basically unchanged or slightly reduced, the concentrate grade reached 64.32%. In order to continue to improve the grade of the concentrate, a fine screen regrinding system was built at the end of 1977, and four ф2.7×3.6m regrinders, three-stage fine screens and corresponding ancillary facilities were installed, with an investment of 4.426 million yuan. After the expansion, the iron concentrate grade will reach over 66%. The raw ore processing capacity of the magnetic separation workshop of Anshan Iron and Steel Gongchangling Mineral Concentrator is 5.6 million t/a. There are 14 series of ф2.7×3.6m ball mills, which were put into production in 1959. After the magnetic separation workshop was put into operation, the concentrate grade was between 61 and 63%. In the second half of 1978, the process was transformed and a fine screen regrinding process was adopted. Six ф2.7×3.6m regrinders and 195 fine screens were added. It was put into operation at the end of 1978, and the transformation cost was approximately 7.78 million yuan. After the transformation, the concentrate grade increased from 62.86% to 65-66%. In April 1978, Anshan Mining Design Institute established the basis for the cation reverse flotation industrial test at Anshan Iron and Steel Sintering Plant. On the project, a regrinding and re-selection workshop was designed to process 1.15-1.2 million t/a of the plant’s rough concentrate and obtain a reverse flotation final concentrate of 1.05-1.1 million t/a. The operation recovery rate was 97-08%, and the final concentrate was obtained. The ore grade has been increased from 62 to 63% to 66 to 68%, and the total design budget investment is 5.16 million yuan. The above is an example of the renovation of an old factory. The infrastructure cost for a new mineral processing plant also increases with the increase of the concentration depth. Sometimes a variety of technical solutions can be adopted to improve the depth of ore selection. Each solution has different production processes, required infrastructure and operating expenses, and different selection indicators. This requires detailed technical and economic comparison. For example, in May 1988, the Design Institute of Anshan Iron and Steel Mining Company provided four feasible plans for the roasting magnetic separation concentrate project of Qidashan Ore Concentration Plant and carried out technical and economic demonstrations. Qidashan roasting magnetic separation process is the second phase project of Qidashan mineral processing plant. It was completed and put into operation from April 1971 to April 1973. It is equipped with ф3.6×4m and 5 ball mill series. At present, systems No. 1, 2, and 3 are two-stage continuous grinding-dehydration-magnetic separation-fine screening processes, and systems No. 4 and 5 are stage grinding-magnetic-gravity-magnetic processes. Statistical indicators in 1987: raw ore The iron content is 30.1%, the iron content of the concentrate is 61.5%, 62.5% after the secondary dewatering tank, and the recovery rate is 78.52%. According to the requirements of Anshan Iron and Steel’s “Seventh Five-Year Plan” plan, the grade of Qidashan roasted magnetic separation concentrate must reach above 64%, and the metal recovery The rate is over 74%. The ore properties and process flows of each concentrator are different, and the investment costs required to improve the concentrate grade vary greatly. The Dashihe dressing plant only spent more than 1.6 million yuan around 1977, and the concentrate grade was increased to 67-68%. The Dagushan and Gongchangling dressing plants required several million yuan, and the concentrate grade reached 65-66%. As for Qi If the Dashan dressing plant achieves the same grade, the cost of transformation will increase. [next] (2) The impact of other separation indicators 1. The impact of increasing concentrate grade on the metal recovery rate of the ore dressing plant. Changes in the metal recovery rate of the ore dressing plant affect the utilization of mineral resources and the ore consumption per unit of pig iron. Increasing the metal recovery rate can reduce the mining and selection expenses per ton of pig iron and reduce the cost of pig iron. Reducing pig iron consumption can also reduce mine investment per ton of pig iron and improve investment results. The raw ore consumption of pig iron per ton can be calculated by the following formula:

In the formula, P raw——the amount of raw ore to be mined for smelting pig iron per ton, t/t; a——the grade of raw ore mined, %; ω——the recovery rate of ore dressing metal (actual recovery rate).%; (The difference between theoretical recovery rate and actual recovery rate varies with the mineral processing method and management level. Generally, the difference between magnetic separation method is about 1.5%; the difference between roasting magnetic separation method is about 2%; the flotation method is about 3% difference) K1———— Metal loss coefficient during the sintering and smelting process of ore (non-recyclable); K1=3% when sintered ore is put into the furnace, K2=2-3% when natural ore is put into the furnace, K2————The coefficient of ore during crushing, beneficiation, transportation and other processes Loss coefficient (non-recyclable); K2=4% when lean ore dressing is put into the furnace, K2=2% when natural lump ore is put into the furnace, when Fe generation=0.94, K1=0.03, K2=0.04 is selected, in the above formula

It can be seen that the raw iron ore consumption per ton of pig iron is inversely proportional to the metal recovery rate. [next] When raw ore with a grade of 30% is selected, the recovery rate increases from 80% to 81%, and the original ore consumption P per ton of iron changes to:

The difference between the two is 4.762-4.695=0.067t/t When the raw ore grade is 30%, the ore dressing sheet metal recovery rate is increased by 1% from 80%, and the iron ore consumption per ton is reduced by 52kg; when it is increased by 1% from 70%, the iron ore consumption per ton is reduced by 67kg ,the lower the recovery level, the greater the ,impact of the change. Changes in ore consumption will affect the mining and dressing costs per ton of pig iron. Taking the impact on the cost of pig iron as an example, the recovery rate increases from 70% to 1%. If the ore is a large deposit that is easy to mine and select, it is assumed that the mining cost per ton of raw ore is 8.50 yuan, and the processing fee for each ton of raw ore is 9.80 yuan. The recovery rate increases by 1%, and the mining and sorting cost per ton of pig iron is reduced by 87.15-85.92=1.23 yuan. If the ore is difficult to mine and select, if the ore mining cost is 18.00 yuan and the raw ore processing fee is 15.00 yuan per ton, the impact on the cost of pig iron will be greater. The cost change of pig iron per ton is 157.15-154.94=2.21 yuan. From the above analysis, it can be seen that the recovery rate of mineral processing metal is not only an important economic indicator of the mineral processing plant, but also an important economic indicator of the entire metallurgical complex. It is as important as the concentrate grade. The grade reflects the quality of the product, and the recovery rate reflects the quantity of the product. The two cannot be neglected. Especially for some mineral processing plants with high mining costs, difficult mineral processing and low recovery levels, we should pay close attention to the changes in metal recovery indicators after ore selection. Whether the recovery rate will decrease after ore beneficiation depends on the depth of ore beneficiation and the measures taken to improve the concentrate grade. The changes in the recovery rates of some domestic mineral processing plants after improving the concentrate grade are introduced as follows: Shougang Dashihe Mineral Processing Plant originally designed 7 series of ф2.7×3.6m ball mills with an annual raw ore processing capacity of 400.75 million tons. In April 1977, Install a section of fine screen to realize the self-circulation and regrinding process of fine screen. In order to increase the capacity of the dressing plant, four new series of the same model and corresponding ancillary facilities were expanded in 1975. They were all put into operation in 1978, and a section of fine screen was installed in June 1979. The total processing capacity of the dressing plant is 6.5 million tons. To improve the screening efficiency of fine screens, the old systems (except No. 1 and No. 2) were gradually changed to two-stage fine screens in 1980. In the same year, the magnetic separators before filtration of series 1 to 11 were changed to double-cylinder magnetic separators. Before 1976, the concentrate grade was about 63.5% during the original production process. In April 1977, the fine-sieving self-circulating regrinding process was implemented and the concentrate grade was significantly improved, reaching 66-67%. In the fourth quarter of 1979, it reached over 68%. In 1980~ It reached 68.5% in the first quarter of 1981, and reached the highest level of 69% in March 1980. [next] The main technical and economic indicators of Dashihe Concentrator on a quarterly basis from 1975 to the first quarter of 1981 are shown in Figure 1.

It can be seen from Figure 1 that the metal recovery rate of Dashihe Concentrator does not decrease with the increase of concentrate grade, and always remains between 80 and 83%. The metal recovery rate was 82.47% in 1985 and 82.64% in 1986. Dashihe Concentrator The reasons why the metal recovery rate does not decrease are: (1) With the improvement of concentrate grade, the process flow has been constantly changing in recent years. For example, the old process was used before 1976, and the fine screen self-circulating regrinding process was adopted in 1977. In 1980, the one-stage fine screen was gradually changed to the two-stage fine screen, and the magnetic separator before filtration was changed to a double-cylinder magnetic separator. machine. In recent years, some measures have been taken, such as changing the particle size of the selected ore from -15mm to -12mm, using magnetic pulleys to improve the grade of the selected raw ore, and using new magnetic agglomeration and re-selection processes. These measures have a certain effect on reducing the tailings grade and improving the metal recovery rate. (2) Changes in ore properties. After 1980, the Dashihe mine stopped production, and the Liuheyu ore with better selectivity began to be put into production, which made the comparison basic Not consistent enough. In order to avoid the above-mentioned effects as much as possible, we conducted regression analysis on the data with less external influence from 1977 to 1979 after the fine-sieving self-circulating regrinding process was put into operation and before the Liuheyu ore was selected, and found that the recovery rate increased with the concentrate grade. The improvement is still affected to a certain extent. The regression analysis results of concentrate grade and theoretical recovery rate in each month from 1977 to 1979 are: Y=122.05-0.60x (3) The analysis results show that under the conditions that the separation process is basically unchanged and the ore properties are basically the same, the concentrate grade When changing between 65 and 68.5%, for every 1% increase in concentrate grade, the metal recovery rate decreases by about 0.6%.