Iron Removal From Leach Solution Of Nickel Oxide Ore By Hematite Precipitation

Leach solutions of nickel oxide ore contain iron,nickel,cobalt,magnesium,aluminum ions.Iron has the highest concentration in the solutions and should be removed firstly to separate iron from other metals.In this paper,the possibility of iron removal by hematite precipitation at 100??160?,reaction temperature,reaction time,material liquid pH,initial concentration of iron ions and other factors affecting the iron deposition product,as well as the influences of magnesium and aluminum ions on iron precipitation were discussed,and the nickel and cobalt losses were explored.Iron precipitates were characterized by X-ray diffraction,Fourier Transform-Infrared Spectroscopy,Scanning electron microscopy and other equipments.The main conclusions are as follows:(1)At the temperatures of 100??160?,PH ?1.4,goethite,basic iron sulfate and jarosite precipitated in priority when Fe3+concentrations was<1.0 g/L,1.0?2.0 g/L,and>9.0 g/L,respectively.With increasing reaction time and temperature,basic iron sulfate and jarosite gradually transformed into goethite,then goethite transformed into hematite gradually.When pH was>1.4,the iron was first deposited as goethite,then gradually converted to hematite.The time of which jarosite converted to goethite was much greater than the time required for which goethite transformed into hematite.Lengthening reaction time,increasing temperature and pH value and reducing the concentration of Fe3+were conducive to form a crystalline product,increase iron removal rate and promote the conversion of goethite to hematite.The higher the degree of crystallization,the better the filtration performance of iron deposits.(2)With decreasing Al3+/Fe3+concentration ratio,iron removal rate showed an increasing trend.High concentrations of aluminum ions have interferences on the deposition of iron to some extent.When Al3+concentration was about 3 times of Fe3+or above,the Al3+ was deposited in the form of(H3O)Al3(SO4)2(OH)6.Under the same concentration of iron ions,changing aluminum ion concentration,the rate of aluminum loss changed little.(3)At 100?140?,when Mg2+ concentration was 10 g/L,the iron deposition products include MgSO4·7H2O.At 100?160?,when Mg2+ concentration was up to 50 g/L,the main phase was magnesium-containing product.The presence of Mg2+promotes the deposition of iron,but does not interfere with the transformation process of goethite to hematite.A part of the magnesium ions may enter into the iron deposition products,limit the growth of crystals of iron deposition products,resulting in difficult filtration.When the deposition product contained magnesium sulfate,filtration performance of deposition products also declined.Adding magnesium ions into ferric sulfate solution containing aluminum ions,iron removal rates increased.(4)At 160?,the surface of iron deposits can adsorb sulfate ions and water molecules,resulting in the negative value of Zeta potential.For the solutions of ferric sulfate containing Ni2+ or Co2+,iron deposits may also adsorb positively charged Ni2+or Co2+,so that Zeta potential changed toward the positive direction.But the sulfate ion concentration was much higher than Ni2+ or Co2+ concentration,thus Zeta potential was still negative.(5)The variation of Zeta potential with the change of deposition time due to the adsorption of Ni2+ and Co2+ were similar.The higher the concentration of Ni2+(or Co2+),the more electrically positive the Zeta potential.Iron deposits on individual The amount of Co2+ adsorption was larger than that of Ni2+ adsorption when the solution contained Co2+ or Ni2+ only.In the solution containing both Ni2+ and Co2+,the competitive adsorption between Ni2+ and Co2+ existed,resulting in the nearly same loss of nickel and cobalt adsorption.A part of Ni2+ and Co2+ can also enter the iron deposits,but the amount of Ni2+,Co2+ entering into the iron deposits was much lower than the amount of Ni2+,Co2+ adsorption,which did not affect the Zeta potential significantly.Adsorption is the main reason for the change of Zeta potential and surface charge of iron deposits and the losses of nickel and cobalt.(6)Temperature,pH and deposition time affect the crystallization behavior of iron deposits,thereby affecting the Zeta potential of iron deposits and the adsorption losses of nickel and cobaltWhen the deposition time was 0.5 h,the adsorption capacity of Ni2+,Co2+,sulfate ions and water molecules by iron adsorption was the strongest.When the deposition time was greater than 3.0h,the adsorption capacity of sulfate ions and water molecules decreased,and Ni2+,Co2+ adsorption capacity did not increase and remain basically unchanged,meanwhile,the attractiveness of the continuous released H+ during iron deposit to the sulfate ions enhanced so that the sulfate ion concentration at the surface of iron deposits gradually decreased,leading to the increase of Zeta potential.The crystallization degree of iron deposits became higher with increasing the solution pH,the adsorption losses of nickel and cobalt were therefore reduced.The hematite was the most stable deposit,and thus Ni2+ and Co2+ adsorption losses were the minimum.The goethite was the relatively stable deposit,and Ni2+ and Co2+ adsorption losses were greater than those of hematite.When the iron deposition product was a mixture of goethite and hematite,which was quite unstable and had the low crystallization degree,the adsorption losses of Ni2+ and Co2+ were the largest.Therefore,in order to separate iron from other metals in the leach liquors of nickel oxide ore and,iron deposition should be conducted under the appropriate conditions to obtain hematite product and prevent losses of nickel and cobalt,and the concentrations of magnesium and aluminum ions should be controlled to prevent the formation of magnesium and aluminum deposits.