Research On Novel Process For Extracting Gold From Refractory Ores With High Arsenic And Sulfur Contents

As one of precious metals, because of excellent physical and chemical features,gold is extensively applied in varies industries, and have significant mean for thedevelopment of the economy. With the development of industry, those easily selectedgold ores have been exhausted. Meanwhile, as all countries pay more attention toenvironmental protection than past, but cyanide is toxic, so cyanidation was expectedto be replaced in future. Besides, people have more demand for gold, it is veryimportant that how to keep sustainable development of gold industry. Refractory goldores account for a large proportion in the whole gold ore resource, and the gold orecontaining high arsenic and sulfur contents is the classic one of refractory gold ores.Therefore, it is necessary to research the technology of processing of this kind of goldore.The raw ore belongs to refractory gold ores with high arsenic and sulfur contents,containing12.8g/t gold,2.56%arsenic and7.52%sulfur. When we adopted differentmethods, such as cyanidation, thiourea process, chlorination process and so on, toleach it directly, the leaching rates were less than16%. So we must take somepretreatment measures to expose the gold. Combining with the relevant literatures andpractical experiments, we would adopt the technology of roasting pretreatment andchlorination process leaching to deal with it. The research of roasting pretreatmentdemonstrate that the process of oxidation roasting at low temperature can effectivelymake the wrapping structure broken so as to expose the gold through the way ofadding oxidizing agents to oxidize pyrite and arsenopyrite wrapping gold. We alsoconducted the single test for the factors which affected the roasting process, andconsidered the influences caused by each element for the final leaching rate. Theoptimum conditions show as follow. the weigh of compound reagent account for18%of raw ore’ quality, its proportion is7:3(between sodium chlorate and ammoniumpersulfate), the roasting temperature is500℃, the roasting time is120minutes, thegold leaching rate can reach80.59%on the above conditions. Meanwhile，we alsoanalyse the mechanism of roasting，the explanation is illustrated as follow：Firstly, itis the decomposition of reagents. Ammonium persulfate break down at150℃~200℃,and release sulfur dioxide and oxygen during this process. Sulfur dioxide generated in the former process act with sodium chlorate, which lead to the product of chlorine.Pyrite and arsenopyrite are oxidized by chlorine and sodium chlorate. Finally, sulfurand arsenic are fixed in the form of sulfur dioxide and arsenic trioxide respectively.The leaching experiments demonstrate that because Sodium chlorate releasechlorine in acid environment, and chlorine is an effective oxidant in chloride leachingsystem. Besides, sodium chlorate also has strong oxidability. Under the actions of all,gold can be leached in the form of AuCl4-. We finished the single factor test andorthogonal test, analyzing the influences of some factors, such as dosage of reagents,leaching temperature, leaching time and so on. The optimum leaching conditionsshow as follow: the dosage of sodium chlorate is90kg/t, dosage of sodium chloride is32kg/t, leaching temperature is80℃, leaching time is120minutes, stirring intensityis700r/min, we received a leaching rate of84.1%. The sequence of influence for theleaching rate was presented as follow: Dosage of sodium chlorate>leachingtemperature>leaching time>liquid-solid ratio>dosage of sodium chloride. We alsoanalyse the leaching process from both aspects of thermodynamics and kinetics,drawing the E-pH figure under the condition of25℃and80℃, the leaching process iscontrolled by the chemical reaction and diffusion control. When the chemical wasdominant, the apparent activation energy is11.43KJ/mol.