Research On Stirred-biooxidation As Pretreatment And Selectively Heapbioleaching Arsenic For Low Au/S Ratio But High-arsenic Gold Cocentrate

The stirred-biooxidation pretreatment is paid the increasing attention due to the reduction of easy-to-treating ores.Though it has been studied so much,there are still some issues hard to resolve,such as narrow application range,independent development technique and the unclear relationship between bacterial and the condition.Focusing on those problems,a series of stirred-biooxidation experiments on a continuous pilot plant scale had been conducted to evaluate whether the "stirred biooxidation-cyanidation" process was fit for the low Au/S ratio but high arsenic-contained gold arsenopyrite/pyrite concentrates in Longnan.Then a new process was designed to reduce arsenic content for Longnan gold concentrate through heap bioleaching.(1)Three bacterias in heap bioleaching lixivium at room temperature were sequenced.They were Acidithiobacillus callus,Leptospirillum ferriphillum,Sulfobacillus thermosulfidooxidans.Due to the poor bacterial activity in bioheapleching process,the S0 passivation was grown to cover the ore surface and then limited the sulphide biooxdation rate.The acidophilic bacterias in the stirred-biooxidation tests was composed of Acidithiobacillus,Leptospirillum,Sulfobacillus and Ferroplasma.The microbial community structure in each tank of stirred biooxdation test was stable and unique,and the sulphide was converted to sulphate promptly.(2)The continuous experiments added nutrient and discharged bacterial metabolites continually to kept a relatively balanced and stable environment.The growth of bacteria was not under the restriction conditions encountered in the batch tests.Compared to the batch tests,the metallurgical results of the continuous pilot tests have shown the better results due to a more diversity and more special bacterial community structure in the continuous tests.Compared to the maximum removal rate of the batch tests(in the initial 10 days),the arithmetic average release rate of total iron in the continuous tests is nearly twice as high.(3)The dissolution behaviours of Fe,S and As showed that a sudden changing experiment condition had a negative effect on the biooxidation rate,which always occurred to the batch test.The average removal rates of the major elements of the arsenopyrite and pyrite concentrate in the secondary reactor-1were much lower than those in the others.The removal rates of iron,arsenic and sulfur in secondary reactor-3 were respectively 5,4 and 1.2 times higher than those in secondary reactor-1.The removal rates in secondary reactor-2 were close to those in secondary reactor-3.The trends of the major element removal rates in continuous tests are different from those in batch tests,first declining in secondary reactor-1 and then sharply rising in secondary reactor-2.(4)The biooxidation of pyrite and arsenopyrite was limited due to poor gas transportation in biological column tests.Elemental sulphur was more likely to be the main products in column leaching tests.Though the S0 was unstable and not tight,it also needed more time to convert it into sulphate.It made selectively leaching arsenic firstly possible.(5)The transformation rules of sulphide to other sulfur species was studied in column bioleaching tests at room temperature and 45?.The content of TS and S-S2-gradually reduced with the column leaching time and the S0 improved firstly then decreased at both temperatures.It was concluded that the S0 oxidation rate was promoted and the effect of S0-rich layer reduced but not eliminated by rising temperature only.(6)The pitting potential of arsenopyrite was almost 0.1 V lower than pyrite in this experiment.Such differences also made arsenopyrite possible to be preferentially and selectively dissolved.As shown by the concentrations of total iron,sulphate and arsenic with time in the bioleaching lixivium,the arsenic reached in balance fastest.It proved that it was preferential dissolved.(7)Almost 50 million RMB for previous fixed capital cost was needed to set up a heap thin-layer bioleaching plan with 500 tons ore treatment capacity per day.The operation cost was about 150RMB per ton concentrate.The heap bioleaching technology was useful to remove arsenic selectively.(8)A plant of stirred-biooxidation process consisted of 3 stages:pre-biooxidation to dissolve Fe,S,As firstly,then cyanide leaching of the biocake and subsequent neutralization the lixivium.A brief description of the treatment flow sheet was provided and some of the main parameters and results of the process were discussed in the paper.It was confirmed that the average 81.40%sulphide removal rate and 92.45%gold extraction was achieved in the continuous tests(7 days total retention time).A techno-economic study of the stirred-biooxidation pretreatment for the high-arsenic refractory gold concentrate was also conducted.Almost 160 million RMB capital cost was needed for a stirred-biooxidation and cyanidation plant with 500 tons daily capacity and the operation cost was about 685 RMB per ton concentrate.The research in this paper will provide the theoretical and technical guidance for the stirred-biooxidization and cyanidation process.The column biooxidation leaching to remove arsenic was benefit for its selectivity.It is a new idea for the exploitation utilization of gold concentrate.A lot of data can be obtained in the continuous test and the oxidation model should be established for other mines.