Theoretic And Process Study On Separating Valuable Metals From Waste Diamond Tools By Hydrometallurgical Methods

With the rapid development of society,the consumption of diamond tools as an efficient cutting tool is increasingly growing.A large number of waste produced from the use and manufacture process has brought great pressure to the environmental protection and resource recycling.Diamond tools contain a lot of diamond particles,copper,iron,zinc and other valuable metals.Therefore,it is of great significance to carry out the research on recycling technology from waste diamond tools.In China,research of recycling valuable metals from waste diamond cutting tools has become relatively late.Most of the existing methods are carried out in the strong acid and oxidant agents system and it has such deficiencies as low metal recovery,serious environmental pollution,serious corrosion of equipment and high processing cost.In view of the national policies about industrial development programming,energy saving and environmental protection,the study is proposed.In order to preliminary separate valuable metals in waste diamond tools,reduce the environmental pollution and improve the recovery rate of metals,it is proposed to use two different processes of ammonia-ammonium sulfate-air leaching?referred to as"one-stage leaching"?and sulfuric acid/alkali melting-water leaching/sulfuric acid-hydrogen peroxide leaching?"three-stage leaching"?to recover waste diamond tools.“One-stage leaching”effectively separated soluble metals copper,zinc from the insoluble metals iron,tin.“Three-stage leaching”is a united separation process.The first stage is to separate iron and zinc,and then to separate tin,and finally to separate copper.The main contents and conclusions of this paper are as follows:The composition of the waste diamond tools was firstly analyzed.The results show that waste diamond tools contain valuable metals which are suitable for economy and environmental protection to recover.The E-pH and lg[Me]_T-pH diagrams of the elements Cu,Zn and Fe in one-stage leaching and the lg[Me]_T-pH diagram of the elements Cu,Zn,Fe,Ni and Sn in three-stage leaching were respectively drawn to analyze the leaching thermodynamics.The results show that Cu and Zn can be selectively leached at first as complex ions under the condition of introducing air in one-stage leaching at the appropriate pH and potential range.The leaching process will be enhanced by increasing the amount of ammonia.The metals of Fe and Zn can be separated from Cu and Sn by acid leaching in three-stage leaching.The leaching will be enhanced by increasing the amount of acid.The one-stage leaching process was studied and the optimum leaching conditions were determined as follow:Leaching temperature 45°C,the leaching time 3h,the liquid to solid ratio 50mL/g,the stirring speed 200rpm,the concentration of ammonia and ammonium sulfate 4.0mol/L and 1.0mol/L,the gas flow 0.2m³/h.Under these conditions,the leaching rates of copper and zinc were 65%and 70%,respectively.Kinetics analysis shows that the leaching process is controlled by mixing reaction.The activation energy is109.50 kJ/mol and the copper leaching process is controlled by the surface chemical reaction below the temperature of 35°C.The activation energy is 38.33 kJ/mol and the copper leaching process is controlled by diffusion below the temperature of 35°C.Three-stage leaching process was also studied and the suitable leaching conditions were determined.At the first stage,3.0mol/L sulfuric acid as leaching agent was adopted and the leaching rates of the copper,iron and zinc were 0.343%,95.13%and 76.48%respectively.At the second stage,the extraction of Sn with the method of alkali melt and water leaching was carried out.Under the optium conditions,the mean value of leaching rate of 3 times repeat experiment was maintained at about 91%.At the last stage,the copper leaching rate was 92.55%with the leaching agents of sulfuric acid and hydrogen peroxide.The orthogonal experiment of five factors and four levels was carried out at the same time and the primary and secondary order of factors was concluded as follows:the concentration of sulfuric acid>solid-liquid ratio>leaching time>the dosage of hydrogen peroxide>leaching temperature.The optimal experiment scheme is:A₄B₄C₂D₁E₄,namely,the concentration of sulfuric acid 3mol/L,leaching time 3h,leaching temperature 40?,liquid-solid ratio 5:1,the dosage of hydrogen peroxide 20ml.The experiment results are consistent with those of single factor experiment.One-stage leaching and the third step sulfuric acid-hydrogen peroxide leaching of three-stage leaching are related to oxidation leaching process.Oxygen in the air is introduced through air compressor in one-stage leaching.The oxygen concentration in the solution is low,difficult to contact with the surface of metal.It is easy to float to the surface of the solution in the form of large bubbles,resulting in low efficiency of air oxidation leaching,and low leaching rate of copper and zinc.Although hydrogen peroxide was adopted in the third step sulfuric acid-hydrogen peroxide leaching of three-stage leaching and the leaching rate of copper was high,the hydrogen peroxide is costly and the residue is not easily erased in the solution,the subsequent treatment is unfavorable.Therefore,a micro-bubble reactor for air oxidation leaching was developed in this paper to improve the oxygen contact probability with the solid reactant in the solution and to improve the leaching efficiency.The effects of structural parameters of Venturi injection pump?the core part of the micro-bubble air oxidation reactor?such as venturi inlet cone angle,outlet cone angle,the total length of the throat and the throat diameter at the throat corner on the inner wall pressure of the flow field were simulated by CFD software Fluent.The parameters of maximum negative pressure were determined as follows:the inlet cone angle 10°,outlet cone angle 10°,the total length of the throat 140mm and the throat diameter at the throat corner 6 mm.Based on the optimized parameters,the Venturi injection pump was prepared to assemble a simple micro-bubble air oxidation reactor.The ammonia leaching copper with micro-bubble air oxidation reactor in small industry test was explored.The optimum leaching conditions were as follows:reaction time 6h,reaction temperature 40?.Under this condition,the copper leaching rate of is 95.34%.,It is expected to be efficient alternative equipment for oxidation leaching because of its high speed and efficiency.Three-stage leaching has a significant advantage over one-stage leaching.The recovery rate of copper,iron and tin is above 90%and zinc is about 80%.It is convenient to separate metal products from the leaching solution.