Research On The Bioleaching Of High-magnesium Nickel Sulfide Ore At Elevated PH

This paper is devoted to solve the problem of huge sulfuric acid consumption and large amount of iron and magnesium dissolution during the normal bioleaching process of high-magnesium nickel sulfide ore.Detection methods like MLA mineral composition analysis,Scanning electron microscope(SEM),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS)and high-throughput sequencing were used to discover the mechanisms for the bio-oxidation and decomposition of pentlandite and the dissolution of olivine and serpentine during bioleaching.Based on the mechanism studies,a novel method of bioleaching at elevated pH was proposed and the process conditions were explored.The efforts of H+,Fe3+,temperature and leaching bacteria on the bio-oxidation and decomposition of pentlandite were studied.H+could promote the break of Ni-S bond and Fe-S bond.Fe3+ could oxidize S2-and S22-into Sn2-and S0.The function of leaching bacteria could be divided into two aspects:Fe3+regeneration and oxidizing Sn2-/S0.During the bioleaching of pentlandite,Fe dissolves faster than Ni.And the oxidation and dissolution rate of S is the lowest.Iron transformed through a(Ni,Fe)9S8? Fe2+?Fe3+?KFe3(SO4)2(OH)6 pathway.Nickel experienced a transformation of(Ni,Fe)9S8?NiS?Ni2+.Sulfur modified through the pathway of S2-/S22-?Sn2-?S0?SO42-.The bacterial communities of leaching bacteria adsorbed on the mineral surface were different at different leaching systems.At normal pH value,the leaching bacteria adsorbed on the mineral surface were mainly sulfur-oxidizing microorganisms.At elevated pH value,the mineral surface was covered by jarosite.Therefore,more iron-oxidizing microorganisms were adsorbed on the mineral surface as sulfur was not available.During bioleaching,two product layers(sulfur rich layer and jarosite layer)formed on the surface of pentlandite grains and the rise of pH value would accelerate the process.However,no evidence for the inhibition of the passivation layers was shown in the bioleaching of pentlandite.The bioleaching of pentlandite could be achieved at elevated pH value.Shrinking core model(SCM)was employed to carry out the kinetics studies of Mg2+dissolution from olivine and serpentine during bioleaching.The influence of temperature,pH and mineral particle size was studied.The most influential factor on the dissolution of Mg2+ from olivine and serpeitine was found to be temperature,followed by pH value and particle size.The controlling step for the dissolution of Mg2+ from olivine was the interfacial chemical reaction between solid and liquid.During the reaction,the silicon oxygen tetrahedron condensed into SiO2 and fell off the surface of the mineral,causing a core shrinking process.The controlling step for the dissolution of Mg2+ from serpentine was internal diffusion.During the reaction,the silicate skeleton was difficult to be destroyed and a product layer appeared on the mineral surface,which hinders the further reaction.Kinetics studies suggested that bioleaching at elevated pH value could effectively inhibit the dissolution of Mg2+ from olivine and serpentine.The technological conditions of bioleaching for high magnesium nickel sulfide ore were explored.The results showed that the acid consumption had a great influence on the dissolution of magnesium and iron,while the grinding fineness had the greatest influence on the leaching efficiency of valuable metals.The optimum parameters for grinding fineness is 72.11%particle size less than 74 ?m,the acid consumption is 300 kg/t,the pulp density is 5%,the inoculation amount is 12.88%.Under these conditions,the metal leaching efficiency are Ni 89.43%,Co 84.07%,Cu 36.78%,Mg 49.19%,and the total Fe concentration of solution is 0.20 g/L.Compared with normal pH value,the leaching efficiency of nickel and cobalt reached 81.70%and 77.78%respectively at elevated pH value,while the acid consumption decreased from 598 kg/t(ore)to 352.83 kg/t(ore),and the dissolution efficiency of magnesium decreased from 66.53%to 23.54%.Bioleaching at elevated pH could achieve a high leaching efficiency of nickel and cobalt with lower acid consumption and magnesium dissolution.