In recent years, with the rapid development of China's economy, the demand for copper and molybdenum in the market has been increasing day by day. However, the overall situation of copper-molybdenum ore resources in China is not favorable – copper ore resources are scarce, with few rich ores and mostly low-grade ores, and the mining areas are scattered with small quantities. Although molybdenum ore resources are abundant, they are mainly native molybdenum ores, and the grades are relatively low. This article takes a low-grade porphyry copper-molybdenum ore as an example to introduce the ore dressing process.
Sulfide copper-molybdenum ore is one of the main sources of copper and molybdenum metals, mainly found in porphyry copper deposits and skarn copper deposits. Porphyry copper deposits, in particular, are often associated with molybdenite, and the comprehensive recovery of molybdenum must be considered in the process of recovering sulfide copper minerals.
In this example, the porphyry copper-molybdenum ore is a low-grade copper-molybdenum ore with unevenly embedded useful minerals, poor dissociation, and difficulty in separation. The valuable metal elements in the original ore with recovery value are mainly Cu and Mo, and their grades are relatively low. The main metal minerals in the ore are chalcopyrite, molybdenite, pyrite, etc., while the main gangue minerals are quartz, feldspar, sericite, biotite, chlorite, etc.
Currently, both domestic and foreign processing of porphyry copper-molybdenum ores mostly use flotation separation methods for copper-molybdenum. The commonly used methods are: preferential flotation, partial mixed flotation, mixed flotation-copper-molybdenum separation.
In this case, considering the low total sulfur content, close symbiotic relationship between sulfide minerals, complex structure, and fine grain size, a flotation process of mixed flotation-mixed concentrate regrinding-fine selection-molybdenum flotation-copper depression separation is adopted based on the characteristics of the ore. This process can simplify the process, reduce over-grinding of minerals, and thus facilitate separation.
(1) Determination of Grinding Fineness
Experiments have shown that when the grinding fineness of -0.074 mm increases from 60% to 68%, the changes in the grade of copper and molybdenum in the mixed concentrate are not significant, and the recovery rates both reach their upper limits. If the grinding fineness continues to increase, the recovery rates of copper and molybdenum both show a decreasing trend. Therefore, considering the ore dressing indicators and grinding costs, the optimal grinding fineness of -0.074 mm is chosen as 68%. At this fineness, the obtained mixed concentrate has a copper grade of 4.19%, copper recovery rate of 88.58%, molybdenum grade of 0.98%, and molybdenum recovery rate of 79.2%.
(2) Copper-Molybdenum Mixed Flotation
The copper-molybdenum mixed flotation stage is the basis to ensure the recovery rates of copper and molybdenum. The mixed roughing collector needs to have strong capturing ability and good selectivity.
This ore contains a certain amount of easily mudified minerals such as chlorite and sericite. Adding a suitable amount of sodium silicate can disperse and inhibit the mud in the ore. After ore dressing test studies, it is determined that at a grinding fineness of -0.074 mm and 68%, the dosage of the dispersant sodium silicate is 500 g/t, and the dosage of No.2 oil is 40 g/t.
Dodecyl yellow and dodecyl ammonium black are chosen as the collectors for mixed flotation of this sulfide ore. The dosage of dodecyl yellow is 80 g/t, and the dosage of dodecyl ammonium black is 40 g/t. The mixed flotation of copper-molybdenum obtains a mixed concentrate with a copper grade of 4.51%, copper recovery rate of 93.09%, molybdenum grade of 1.23%, and molybdenum recovery rate of 90.42%.
(3) Mixed Concentrate Regrinding and Fine Selection
The mixed concentrate obtained from the full sulfur mixed flotation is subjected to fine selection separation using a process flow that first depresses sulfur and floats copper-molybdenum, and then depresses copper and floats molybdenum.
Grinding tests show that without regrinding, it is difficult to effectively inhibit pyrite, and the grade of copper-molybdenum concentrate is hard to improve. However, if the grinding is too fine, molybdenum is difficult to recover effectively. Therefore, the regrinding fineness is determined to be -0.043 mm, accounting for 90%. The resulting bulk molybdenum concentrate has the same grade of 17.75%, molybdenum grade of 3.6%, copper recovery rate of 81.46%, and molybdenum recovery rate of 67.73%.
Lime is added in appropriate amounts during the fine selection process to separate sulfur from copper. After experimental research, the lime dosage is determined to be 600 g/t.
(4) Copper-Molybdenum Separation Flotation
The copper-molybdenum separation flotation adopts a one-rough-three-fine flotation process, and the final products are molybdenum concentrate. The dosage of flotation dispersants in the separation stage is halved sequentially.
Using sodium silicate alone for the dispersion and inhibition of the pulp has poor effects, and it needs to be mixed with two other reagents. Sodium silicate and sodium hexametaphosphate are used in combination, with a dosage of 80/80 g/t, to achieve good open-circuit flotation indicators for molybdenum concentrate with a grade of 45.66% and a recovery rate of 46.01%. Additionally, adding kerosene during copper-molybdenum separation flotation can effectively improve the separation indicators of molybdenum, but kerosene has a significant defoaming effect, causing insufficient dosage of No.2 oil, which will restrict molybdenum recovery. The experiment determines the kerosene dosage to be 8 g/t.
After copper-molybdenum separation flotation, a molybdenum concentrate with a molybdenum grade of 43.62% and a molybdenum recovery rate of 70.41% is finally obtained. A copper concentrate with a copper grade of 24.25% and a copper recovery rate of 87.14%, and a sulfur concentrate with a sulfur grade of 39.30% and a sulfur recovery rate of 79.08% are also obtained.
For the ore dressing process of porphyry copper-molybdenum ore, it is necessary to obtain a mixed concentrate first, then regrind the mixed concentrate, depress sulfur and float copper-molybdenum, and finally perform copper-molybdenum separation. Throughout the process, two rounds of grinding are required, and the fineness of each grinding should be determined after detailed grinding tests to achieve better results.
