Per second rotations also effect cellular receptors and secretory vesicles. Indirectly it is governed by  reducing proteins which are located at the cell surface, after first time secretion, a reverse osmosis of eletro-positive binding may occur that seep in the metal back through a negative binding.  Add some alkali it will stop the reverse of ion sweeping from the medium.

For bio leaching, the bacteria should be in contact with the source and mild agitation will boost the process as the bacteria will be uniformly distributed. But after a certain rpm, the contact time decreases, therefore decreasing the leaching efficiency.

Attachment efficiency is the key. The optimum rpm is around the value, say 120 rpm, though differs. What to do with the rpm then? Its depends on which region you are in, Newtonian or non-Newtonian. In layman's term, in a turbulent sea, all the possible direction in which we could swim is restricted by turbulent water flow; why it should be different for bacteria or mineral? Therefore, if you make the bacteria-mineral suspension turbulent, the leaching efficiency will decrease as per decrease the rate of bacteria-mineral attachment and complete attachment efficiency. One way to measure these rates could be to plot bacterial count vs rpm. 

There are two opposing effects when the agitation increases: better conditions for gas transfer (oxygen and carbón dioxide)(positive effect) and an increased level of attrition by collisions between mineral particles with attached bacteria that lead to cell lysis and destruction (negative effect); the last one has two negative effects, a decrease of viable microorganisms and secretion into the culture medium of organic material from bacterial lysis, with growth inhibitory effects of autotrophic microorganisms.. When a variable exerts two opposing effects, you can locate the optimal value.