Study On The Process Of Separation And Extraction Of Gold From Chlorination Roasting Of Complex Gold-bearing Pyrite

The gold extraction from complex Au-bearing pyrite ore is studied.A two-stage roasting method is applied in this research,of which the mineral phase reconstruction is achieved by the first stage preroasting and medium-temperature chlorination roasting is further carried out.After the chlorination roasting,gold can be volatilized in the form of chloride from the calcine.Thus,a new technique of low energy consumption is developed for efficient separation and recovery of gold from the refractory gold pyrite ore.The main contents of this thesis are as follows:(1)An appropriate chloride agent is selected for chlorination roasting.The effects of mixing methods as well as roasting methods and the additives are studied on the chlorination roasting process.NaCl is determined as the chloride agent and the dry mixing as well as pelletizing without additives is also selected for the chlorination roasting of Au-bearing pyrite ore.(2)Based on the thermodynamic analysis,the decomposition of NaCl,the oxidation of sulfur and the volatilization of gold in the roasting of pyrite are studied.It's proved that the decomposition of NaCl can be promoted by SO2 which is the oxidizing product of pyrite under rich oxygen condition.The gold volatilization is further accelerated.The optimum direct chlorination roasting conditions are determined as follows: the temperature of 1000 ?,the roasting time of 2 h,the NaCl dosage of 0.2 mol/g-ore.Under the conditions stated above,the extraction of gold is achieved as higher as 95.37%.(3)The kinetics of direct chlorination roasting of Au-bearing pyrite ore is studied.The results show that the volatilization of gold increases with the increase of roasting temperature as well as the dosage of NaCl rapidly.The process follows the shrinking unreacted nuclear model.The volitilzation of gold is controlled by internal diffusion and the apparent activation energy for the roasting is calculated as 19.066 kJ.mol-1 on the basis of Arrhenius equation.The kinetic equation can be described as:1-3(1-x)23?+ 2(1-)= 3.02×10-2 exp [-19066 /(RT)] ? t.(4)The optimum two-stage roasting process is determined as follows: the first stage roasting,the temperature of 550 ?,the roasting time of 1 h;the second-stage chlorination roasting,the temperature of 850 ?,the roasting time of 2 h,the NaCl dosage of 0.2 mol/g-calcine,the SO2 dosage of 0.2 mol/g-calcine.A certain quantity of SO2 gas as the the first-stage roasting product can be introduced into the chlorination roasting.Under the conditions as stated above,the volatilization of gold is achieved as higher as 96.28%.Thus,the effective gold extraction is achieved by chlorination roasting under a relatively low temperature.(5)Based on the L16(45)orthogonal experiments,the effects of the first-stage roasting temperature,the second-stage chlorination roasting temperature,the dosage of NaCl and SO2 on the volatilization of gold are discussed.The range analysis as well as variance analysis shows the principal order is as follows: the dosage of NaCl>the second-stage chlorination roasting temperature>the first-stage preroasting temperature> the dosage of SO2>chlorination roasting time.