To ensure optimal reagent effectiveness, the location and method of reagent addition should be rationally selected based on the ore properties, reagent properties, and process requirements.

The choice of reagent addition location is related to the purpose and properties of the reagent. Generally, a pH adjuster is added first, which can be added to the ball mill. This allows the inhibitor and collector to function in a suitable pH pulp, and also eliminates certain “inevitable ions” harmful to flotation. Inhibitors should be added before the collector, usually also to the ball mill, allowing the inhibitor to react with the fresh surface of the inhibited minerals as early as possible. Activators are often added to the stirred tank, where they are stirred with the pulp for a period of time to promote interaction with the activated minerals. Collectors and frothers are added to the stirred tank or flotation machine, while poorly soluble collectors (such as cresol black, white powder, kerosene, etc.) are often added to the grinding mill (to promote dispersion and increase the interaction time with the minerals).

The common order of reagent addition depends on the situation. For raw ore flotation, the order is: pH adjuster – depressant – collector – bubbling agent. For minerals whose flotation is inhibited, the order is: activator – collector – bubbling agent.

There are generally two methods of reagent addition: one-time addition and batch addition. One-time addition involves adding all the reagents at once before roughing. This method results in a high concentration of reagents and is convenient. One-time addition is often used for reagents that are easily soluble in water, will not be carried away by froth, and are not easily inactivated in the pulp, such as lime and soda. Batch addition involves adding reagents in several batches along the roughing, cleaning, and scavenging lines. Generally, 60%–70% of the total amount is added before flotation, with the remainder added in several batches at appropriate locations. For the following situations, batch addition should be adopted:

(1) Reagents that are easily oxidized, decomposed, or react and deteriorate, such as xanthate and sulfur dioxide gas;

(2) Reagents that are poorly soluble in water and easily carried away by foam, such as oleic acid and fatty amine collectors;

(3) Reagents with strict dosage requirements, such as sodium sulfide. Excessive local dosage of such reagents will have the opposite effect. The reagent addition locations and dosages designed by the flotation plant according to the above principles should not be easily changed during production operations. However, in sites with long flotation lines, in emergency situations such as flotation machine “runaway,” “sinking,” deterioration of concentrate quality, or large amounts of metal entering the tailings, it is permissible to temporarily add some reagents at appropriate locations to minimize losses as quickly as possible. However, the cause of the abnormality should be analyzed promptly, and adjustments should be made as soon as possible to bring production back to normal.