In Laboratory, the quality of the concentrate floated in the 1^st minute of rougher improves if reagent/collector is stage-added.  Stage-adding collector involves adding ½ the total dosage to the 1^st cell + ¼ to the 2^nd and ¼ to the 3^rd or 4^th cell.  It can be expected a similar metallurgical behavior could be obtained in-plant.

Flotation circuit sampling have indicated the concentrate floated from the 1^st cell of the rougher circuit to also be over 61% Zn.
Some reagent optimization work could improve this number.
Other flotation plant sampling have indicated the concentrate floated from the 1^st cell of the 1^st cleaner circuit to also be over 62% Zinc.
Some reagent optimization, similar to in-laboratory, could improve this number.

Learn more in reading The Effect of Reagent Addition Points and Aeration on the Flotation Performance of Sulphide Minerals