The purpose of reasonable addition of reagents is to ensure that the reagents can effectively interact with minerals, thereby achieving selective collection of minerals. In addition, maintaining the maximum efficiency and optimal concentration of reagents in the slurry is also crucial for the stability of mineral processing indicators. Therefore, it is necessary to select the appropriate dosing location and method based on the characteristics of the ore, the properties of the chemicals, and the process requirements.
In practical operation, the selection of dosing points is closely related to the usage of the reagent and also to the dosing points of the reagent that will be replaced. Usually, adjusters (such as lime) are added to the grinding machine to eliminate the activation or repression of "inevitable" ions that may have harmful effects on flotation. Depressants should be added before the collector and can generally be added to the mill or mixing tank. Activating reagents are usually added to the mixing and stirring tank. As for the collector and frother, they are usually added to the buffer tank in front of the mixing tank or flotation machine. For some slowly acting collectors (such as cresol diphenyl dithiophosphate, Dithiophosphate 25, kerosene, etc.), in order to promote their dispersion in the slurry and effective interaction with minerals, and prolong their interaction time with minerals, they are sometimes added to the grinding machine.
The common order of adding reagents during flotation of raw ore is: adjusting reagent - depressant - collector - frother; When flotation of minerals is depressed, the dosing sequence is: activator - collector - frother.
In addition, the selection of dosing points also needs to consider the properties of the ore and other specific conditions. For example, in some copper sulfide flotation plants, adding xanthate to the grinding machine has improved the copper separation index. In addition, when installing a single cell flotation machine in the grinding cycle to recover dissociated coarse ore particles, in order to increase the action time of the collector, it is also necessary to add chemicals to the grinding machine.
In terms of dosing methods, flotation reagents can be added in two ways: one-time addition and batch addition.
One time addition refers to adding a certain reagent to the slurry at once before flotation, so that the concentration of the reagent at a certain operating point is higher and it is more convenient to add. In general, one-time dosing is often used for reagents (such as soda, lime, etc.) that are easy to dissolve in water, are not easy to be taken away by foam machinery, and are not easy to react in the slurry and fail.
Batch dosing refers to adding a certain reagent in several batches during the flotation process. In general, 60% to 70% of the total amount is added before flotation, and the remaining 30% to 40% is added in several batches to appropriate positions. This batch dosing method can maintain the concentration of reagents throughout the flotation operation line, thereby stabilizing the beneficiation indicators.
For the following situations, batch addition should be adopted:
(1) For those agents that are difficult to dissolve in water and easy to be taken away by foam (such as oleic acid, aliphatic amine collectors).
(2) Reagents that are prone to react or decompose and become ineffective in mineral slurry. For example, carbon dioxide, sulfur dioxide, etc., if only added at one point, will quickly react and fail.
(3) For reagents that require strict dosage control. For example, if the local concentration of sodium sulfide is too high, it will lose its selectivity.
The duration of action of reagents varies, and commonly used reagents in practice can be determined based on experience. For example, pine oil requires 1-3 minutes of action time, while xanthate requires 1-4 minutes.
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