Experimental Study And Numerical Simulation Of Cadmium Removal By Variable Speed Stirring In Hydrometallurgy Of Zin

Zinc-containing dust,a by-product of the iron and steel industry,is a valuable secondary resource,containing mainly valuable elements such as Fe,Zn,Cu,Co and Cd at a content even higher than the grade of the primary ore industry.The separation and extraction of valuable metal elements from zinc-containing dust by the hydrometallurgy of zinc is of great significance for the high-value recycling of resources.In the actual industrial production process,mechanical stirring technology as the main control link of the purification process,there are still problems such as low purification efficiency,low recovered metal grade and single control method.Therefore,this paper builds a wireless precision-controlled function waveform variable speed mixing device with point-to-point data transmission between an industrial control computer and a microcontroller for the intensification of the zinc powder purification process in hydrometallurgy of zinc with zinc-containing fumes.By optimising the mixing control technique,the reaction mechanism and fluid mixing characteristics of the purified cadmium are investigated,revealing the coupling between the fluid flow pattern and the chemical reaction.In this paper,the motor driven mixing paddle is controlled by a single closed-loop static differential-free speed control system with pulse width modulation system for variable speed mixing based on arbitrary function waveforms.The effect of variable speed stirring on the purification rate and cadmium grade was investigated.Numerical simulations were carried out to investigate the flow pattern changes in the flow field of the functionally variable speed mixing.When K_P(Proportionality factor)=0.012 and T_i(Integration factor)=100,the anti-disturbance of the stirring speed is achieved,which improves the stability of the system and makes the device more robustness.When the purification rate was 92%,the purification time was reduced by about 40%for the variational sine function mixing compared to the uniform speed mixing and by about 33.3%compared to the variational trapezoidal function speed mixing;only the variational sine mixing could result in a purification solution containing less than 10mg/L of cadmium and a cadmium grade of more than 88%.At a maximum stirring speed of 70 rpm,the turbulence kinetic energy of the variable speed stirred fluid was increased by 50.61%and the dissipation rate of the eddy kinetic energy was increased by up to 62.05%.In the process of variable speed stirring of the function waveform,the axial convection effect can disturb the cadmium sponge for recombination to reduce the microporous structure and improve the cadmium grade.The radial convection effect can increase the contact area between zinc powder and cadmium and improve the purification rate.Moreover,the smaller the stirring period of variable speed stirring of the function waveform,the homogenization effect of fluid mixing is positively correlated with the purification rate and cadmium grade.This paper provides a theoretical basis for the technology related to variable speed stirring control process.