Study On The Extraction Of Gold From Gold Mine Tailings By Ultrasonic Enhanced Fenton Method

With the increasing demand for gold,there are less and less gold mine resources on the earth.Therefore,it is very important to recover gold efficiently from gold mine tailings.At present,the common methods for the resource recovery of gold mine tailings at home and abroad are gravity separation,mercury mixing,cyanidation,flotation,thiourea and bromination,but they have their own limitations.In view of the shortcomings of the existing gold leaching methods,this paper combines ultrasonic and Fenton oxidation technology for the gold leaching process of gold mine tailings,and the specific research contents are as follows:(1)The effects of hydrogen peroxide concentration,ferrous ion concentration,temperature,ultrasonic power,average particle size,solid-liquid ratio and leaching time on the extraction of gold mine tailings by ultrasonic enhanced Fenton process were studied.Through single factor experiment,the ultrasonic enhanced Fenton method can achieve the best leaching effect when the concentration of hydrogen peroxide is 2.1 mol·L-1,the concentration of ferrous ion is 0.45 mol·L-1,the temperature is 338.15 K,the ultrasonic power is 360 W,the average particle size of gold mine tailings is 8.71?m,the L/S is 40/7 mL·g-1,and the leaching time is 30 min,and the maximum leaching rate is 94.30%.On this basis,we have carried out the gold leaching control experiment of ultrasound alone and Fenton alone.It was found that the gold leaching rate of ultrasonic enhanced Fenton was 3.46 times of that of single Fenton and 15.04 times of that of single ultrasound.(2)Based on the single factor experiment,the mechanism of ultrasonic enhanced Fenton gold leaching was studied.The results show that the·OH produced in the experiment has an important influence on the leaching of gold mine tailings.The higher the concentration of·OH is,the more it promotes the leaching of gold.Excessive hydrogen peroxide and ferrous ions will lead to the reduction of the production rate and utilization rate of ·OH in the reaction system,which will reduce the leaching rate of gold.The results of scanning electron microscopy(SEM),Brunner—Emmet-Teller measurements(BET),X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS)show that the gold mine tailings are more loose after reaction,and there are etched pits on the mineral surface.In the case of no obvious change in particle size,the specific surface area changes from 3.8 m2·g-1 to 14.6 m2·g-1,which increases by 3.8 times,and the pore volume changes from 0.019 cm3·g-1 to 0.030cm3·g-1,which increases by 1.6 times.The comparison shows that the difference in mineral particle size before and after the reaction is not significant,which can be regarded as unchanged.After the reaction,Au in the tailings of gold mine has not yet peaked.It is speculated that 94.30%of gold in the tailings of gold mine is leached from the tailings of gold mine in the form of ion(Au+/Au3+)after being strongly oxidized.Therefore,the residual gold content in the tailings is so low that it is not detected.In addition,according to the mechanism of ultrasonic enhanced Fenton gold leaching,the micro process of ultrasonic enhanced Fenton gold leaching was simulated.The process of ultrasonic enhanced Fenton leaching gold from tailings is in accordance with the shrinking core model commonly used in hydrometallurgy.Through the established model and experimental data,the apparent activation energy Ea of leaching is 42.50 kJ·mot-1.Compared with the solid film diffusion control,the leaching process is controlled by the interface chemical reaction,and the kinetic equation of ultrasonic enhanced Fenton leaching process is obtained,which provides theoretical guidance and basic data for ultrasonic enhanced Fenton leaching.(3)According to HJ/T 300-2007-solid waste leaching toxicity method-acetic acid buffer solution method before and after the reaction of gold mine tailings,the residual amount of heavy metals in the leaching solution of gold tailings before and after ultrasonic enhanced Fenton treatment was studied.It was found that the concentrations of As,Cr,Cu,Ni,Pb,Zn,Cd and Ag in the leaching solution were lower than the standard limits.Compared with the gold mine tailings before reaction,As,Cr,Cu,Ni,Pb,Zn,Cd and Ag in the leaching solution of gold mine after reaction were reduced by 69.41%,96.29%,91.68%,89.70%,89.35%,81.61%,78.33%and 97.59%respectively.Ultrasonic enhanced Fenton can effectively reduce the leachable amount of heavy metals in gold mine and reduce the potential environmental risk.In addition,the leaching solution of gold mine tailings before and after the reaction was used to culture rice and wheat seeds.Through the determination of germination index and growth index of two kinds of seeds,it is found that the gold mine tailings treated by ultrasonic enhanced Fenton can reduce the inhibition of rice and wheat seeds germination to a certain extent.However,with the increase of the concentration of the leaching solution from the gold mine tailings,the dry weight of the underground and aboveground parts of rice and wheat seedlings decreased.The higher the concentration of eluate,the more toxic it will be to rice.Compared with wheat,the effect of gold mine tailings eluant before and after the reaction on rice growth was less.