In order to determine the effect of shear friction caused by different pulp concentrations on the biooxidation performance of leaching bacteria, silica microsphere particles (100 μm) with a particle size close to that of ore particles were used instead of ore as the solid phase to study the biooxidation performance of two moderately thermophilic bacteria Leptospirillum ferrooxidans (L.f) and Acidithiobacillus caldus (A.c). The tolerance of these two moderately thermophilic leaching bacteria to shear friction was preliminarily determined. The density of silica microspheres was close to that of pulp, giving them a similar solid phase sedimentation rate. They were stable in the acidic environment of bioleaching, did not release metal ions or consume nutrient substrates, and can maintain the stable microenvironment required for the metabolism of bioleaching bacteria. In this study, a down-pressure four-pitched impeller stirred tank reactor was used for testing. It was found that for L.f, with the increase of silica solid holdup, the increase rate of redox potential value slowed down, the reaction time extends, and its oxidation performance was reduced by shear friction. When the solid holdup reached 25% (w/v), L.f showed obvious damage. As a sulfur-oxidizing bacteria, an increase in solid holdup also resulted in intensified shear friction within the A.c reaction system, as well as a reduction in bacterial oxygen uptake rate. However, when excessive elemental sulfur powder was initially added, residual sulfur powder remained when the oxidation of A.c was completed. Even at 30% (w/v), where oxidation time was significantly prolonged, the bacteria still maintained good oxidation activity. The addition of the baffle was beneficial to the uniform dispersion of the gas and improved the dissolved oxygen concentration and oxygen mass transfer efficiency, but the shear friction effect was enhanced accordingly, causing further damage to bacteria. As the solid holdup increased to 20% (w/v) and above, the baffles inflicted severe damage on L.f, resulting in a marked increase in oxidation time. For A.c, the baffle improved the mixing uniformity of elemental sulfur powder, and effectively broke up bubbles, which was conducive to the uptake of oxygen by A.c, and exerted a certain compensatory effect on the oxidation reaction. At 30% (w/v), the oxidation time of A.c was not significantly prolonged.