Zebiao Zhang

Leaching zinc from spent catalyst: Process optimization using response surface methodology

The spent catalyst from vinyl acetate synthesis contains large quantity of zinc. The present study attempts to leach zinc using a mixture of ammonia, ammonium carbonate and water solution, after microwave treatment. The effect of important parameters such as leaching time, liquid/solid ratio and the ammonia concentration was investigated and the process conditions were optimized using surface response methodology (RSM) based on central composite design (CCD). The optimum condition for leaching of zinc from spent catalyst was identified to be a leaching time of 2.50 h, a liquid/solid ratio of 6 and ammonia concentration 5.37 mol/L. A maximum of 97% of zinc was recovered under the optimum experimental conditions. The proposed model equation using RSM has shown good agreement with the experimental data, with a correlation coefficient (R(2)) of 0.95. The samples were characterized before and after leaching using X-ray diffraction (XRD), nitrogen adsorption and scanning electron microscope (SEM).

Effects of microwave pretreatment on zinc extraction from spent catalyst saturated with zinc acetate

Abstract A new technology for microwave pretreatment of spent catalyst on Zn extraction by HCl leaching was proposed and the temperature-change curve of spent catalyst under microwave irradiation was measured. The influence of microwave pretreatment temperature and microwave irradiation time on zinc extraction was investigated and the mechanism of microwave pretreatment for spent catalyst was analyzed. The results show that microwave pretreatment can greatly enhance the leaching rate of Zn. The Zn extraction reaches 96.58% under the conditions of microwave pretreatment temperature of 950 °C and the microwave irradiation time of 12 min. The blocked pores of spent catalyst can be opened through microwave pretreatment, increasing the contact area of leaching reagent and zinc.

Non-isothermal microwave leaching kinetics and absorption characteristics of primary titanium-rich materials

Abstract The non-isothermal leaching kinetics of primary titanium-rich material by microwave heating was investigated, and the temperature-pressure curves of leaching system and microwave absorption characteristics of mixture solutions before and after leaching were measured. The research of non-isothermal kinetics was evaluated by the leaching rate of Fe and the total apparent velocity equation of the non-isothermal kinetics of leaching for primary titanium-rich material by microwave heating was obtained. It is shown from the temperature-pressure curves that the high temperature and high pressure of closed leaching system are favorable to the enhancement of the leaching rate of Fe. Microwave absorption characteristics of mixture solutions before and after leaching show that there are abrupt changes of microwave absorption characteristics for 15% HCl solution and the mixture solution after leaching by 20% HCl.

Separation and enrichment of elemental sulfur and mercury from hydrometallurgical zinc residue using sodium sulfide

Abstract The separation and enrichment of mercury and the recovery of elemental sulfur from flotation sulfur concentrate in zinc pressure leaching process were carried out by sodium sulfide leaching and carbon dioxide precipitating. The results show that the leaching rate of elemental sulfur is more than 98%, and 98.13% of mercury is enriched in the residue, under the optimized conditions of sodium sulfide concentration 1.5 mol/L, liquid/solid ratio 6:1 and leaching time 30 min at room temperature. In addition, the content of mercury is enriched 5.23 times that in the leaching residue. The elemental sulfur is precipitated from leaching solution under conditions of carbon dioxide flow rate 200 mL/min and blowing time 150 min, while solution is stirred adequately. The recovery efficiency of elemental sulfur reaches 97.67%, and the purity of elemental sulfur is 99.75%, meeting the requirements of industrial first-rate product standard according to the national standard of GB/T 2449–2006 (PRC).