The Study On Comprehensive Utilization Of Kaldo Slag Using Hydrometallurgical Process

A novel hydrometallurgical process was developed to treat Kaldo slag based on its composition and phase characteristics with reference to the current industrial treatment of anode slime. The process mainly includes three steps of pre-treatment, lead separation and barium separation.1. Pretreatment of Kaldo slag1) Two-stage leaching was employed to pretreat the slag since the high content of silicate in it. The purpose of first-stage leaching is pre-desilication. The results showed that the desilication reached90.2%with HC1concentration of1.5mol/L and Na2SO4concentration of1.5mol/L at L/S ratio of5/1and stirring speed of300rpm under room temperature(25℃) for90s, while the leaching of Bi was84.3%and the loss of Pb was only0.5%.2) The purpose of second-stage leaching is to completely remove the base metals in the first-leach residue. The results showed that the leaching of Bi and Si was92.1%and73.6%, respectively, with HC1concentration of2mol/L and Na2SO4concentration of2mol/L at L/S ratio of4/1and stirring speed of200rpm under50℃for40min, while the loss of Pb was only1.6%.3) After two-stage leaching, the content of Si and Bi was reduced to0.13%and0.042%, respectively, corresponding to the removal of Si and Bi97.4%and98.8%. Almost all of the base metals were removed except lead and barium. The total loss of lead was only2.1%.2. Lead separation1) The mixed solution of acetate acid and sodium acetate was used to leach lead from the second-stage leach residue. The results showed that the leaching of lead reached99.1%with acetate acid concentration of1mol/L and sodium acetate concentration of2mol/L at L/S ratio of5/1and stirring speed of300rpm under room temperature (25℃) for2h, leaving only1.34%of lead in the residue.2) The results of lead precipitation using sodium sulphite from lead-rich leach solution showed that the content of lead was reduced to4ppm with excess coefficient of anhydrous sodium sulphite1.25at stirring speed of200rpm under room temperature (25℃) for20min. The recovery of lead reached96.9%with the purity of lead sulphite of97.4%.3. Barium separation1) The Na2CO3solution was use to convert barium sulphate in lead-leached residue to barium carbonate which can be easily leached out by acid. The results showed that the leaching of barium reached95.1%with Na2CO3concentration of400g/L and HCl concentration of2mol/L at L/S ratio of8/1and stirring speed of300rpm under95℃for2h using two-stage counter current leaching, leaving4.56%Ba in the leach residue which was called precious slag.2) The results of barium precipitation using H2SO4showed that the content of barium was decreased to2.92ppm with H2SO4excess coefficient of1and concentration of2mol/L under room temperature(25℃) for0.5h. The recovery of barium reached94.6%with97.5%purity of BaSO4.3) The converted leaching solution can be used to neutralise and precipitate Bi in the first and second stage leach solution, the content of Bi in the residue were5.54%and9.79%, respectively. The recovery of Bi reached90.1%.4. Distribution of gold and silver1) After the treatment of Kaldo slag under optimum conditions, the total weight loss of the slag was92.24%, and the content of gold in precious slag was3064g/T, which means100%of direct gold recovery. The concentration ratio of gold reached14.7.2) The content of silver in precious slag was5.7130%, which means92.36%of direct silver recovery. The concentration ratio of silver reached11.9. The total loss of silver in the whole process was5.52%, corresponding to3.47%,0.60%and1.45%in the step of pre-treatment, lead separation and barium separation, respectively.3) It was found that the tin in the slag has also been concentrated during the whole process. The content of tin in precious slag was36.30%, which means92.20%of direct tin recovery. The concentration ratio of tin reached11.9. The hydrometallurgical process can be used to treat the Kaldo slag for the separation and recovery of metal values such as Bi, Pb, Ba, Sn, Au, Ag. The process exhibits advantages of high concentration ratio and low loss of precious metals, low energy and reagent consumption, low cost and low environmental pollution.