Pretreatment Of Arsenic-bearing Gold Ore With Microwaveassisted Alkaline Leaching

The arsenic-bearing gold ore currently becomes one of the main raw materials for extracting gold.But it also be known worldwidely as the refractory gold ore because of the low cyanide extraction rate.So it is necessary to improve the cyanidation rate of gold by the pretreatment process.In this paper,the arsenic-bearing gold ore was pretreated by the sodium hydroxide leaching under the effect of microwave irradiation,mainly consisting of three parts,as follows.In order to compare with the microwave-assisted leaching,firstly the removal of arsenic in the gold ore by the sodium hydroxide leaching at 100? with water-bath heating was investigated.The results show that part of arsenic in the ore could be removed under the condition and the liquid-solid ratio is the main influencing factors.There is interaction between sodium hydroxide concentration and leaching time and so is the L/S and leaching time.The optimum conditions of sodium hydroxide concentration,reaction time and the ratio of liquid to solid were 10 wt.%,150 min and 6 respectively.Under the optimal condition,the removal of arsenic could reach approximately 82.67%.The analysis results of x-ray diffraction?XRD?revealed that As4S4 were decomposed during the leaching process while the FeS2 and FeAsS were not.The kinetics study of conventional leaching showed that the alkaline leaching of arsenic is controlled by diffusion process and the activation energy of leaching process is 7.549kJ·mol^-1.Leaching of arsenic from gold concentrate ore by sodium hydroxide with the microwave-assisted was studied.The results indicated that the leaching rate of arsenic increased slightly compared to conventional leaching experiments.The main factor affecting the leaching of arsenic is the concentration of sodium hydroxide.There is no interaction between each factors.The optimum conditions under the microwave-assisted was sodium hydroxide concentration of 9.28 wt.%,reaction time of 90 min,microwave power of 700 W and the ratio of liquid to solid of 5.Under the condition,the removal of arsenic is up to 84.59% approximately.The phase change was consistent with the conventional leaching process.The removal of arsenic by air oxidation and sodium hydroxide leaching under the effect of microwave irradiation was investigated.The results show that compared with conventional leaching,the leaching rate of arsenic was not very different and the pretreatment period was shortened significantly.The experiments of orthogonal arrays showed that the sodium hydroxide concentration were the important influence factors.The optimum conditions were sodium hydroxide concentration of 18wt%,reaction time of 90 min,microwave power of 539 W and the ratio of liquid to solid of 5.Under the condition,the removal of arsenic is up to 81.59%.Compared with the former two leaching process,FeAsS was also decomposed but the FeS₂ still exists in the leaching residue.The kinetic study of microwave assisted leaching shows that the leaching process is still controlled by diffusion process.Compared with conventional leaching,when the microwave power was about 539 W,the size distribution of leaching slag changed greatly.The volume fraction of larger particles decreased obviously,and the volume fraction of small particles increased.The SEM diagram of the slag shows that the surface of the mineral particles of the conventional leaching slag is relatively smooth,and the porous surface of the mineral particles appears after the microwave radiation is added.The cyanidation-leaching experiment of gold shown that in the condition of liquid-solid ratio of 5,extraction time of 24 h,cyanide concentration of 0.5%,the gold extraction rate increased from 23.52% to 67.51% when the ore was pretreated by sodium hydroxide leaching.With the addition of microwave radiation,the extraction rate of gold was further increased to 75.21%.