High Value-added And Green Utilization Of Zinc Oxide Ore And Analysis Of Reaction Process

Zinc oxide ore is the secondary ore of zinc and the components are complex.The main zinc phases are zinc silicate(Zn2SiO4),hemimorphite[Zn4(Si2O7)(OH)2 H2O],hydrozincite[3Zn(OH)2·2ZnCO3]and smithsonite(ZnCO3)and so on.The zinc sulfide ore's insufficient makes the utilization of zinc oxide ore urgent and important.Based on the cleaning,effective and comprehensive utilization of zinc oxide ore,this report presents the new idea to achieve the cleaning,effective and comprehensive utilization of zinc oxide ore.This thesis focuses on the research from the following aspects.The strong acid weak base salt(NH4)2SO4 was used to roast the zinc oxide ore to separate Zn form Pb and Si.The exhaust gas was absorbed using H2SO4,and zinc products were gained after purifying the leaching solution.(NH4)2SO4 was return to roasting process through evaporating crystallization.The residue after zinc extraction could be treated by NH4HCO3-HCl conversion method to extracte Pb and Sr.The residue was roasted by NaOH to obtain Na2SiO3 to separate from iron.Then iron was recycled.The Na2SiO3 solution was carbonated using CO2 to produce SiO2 and Na2CO3 solution.The NaOH solution and CaCO3/CaSiO3 precipitate were successfully prepared by causticizing Na2CO3/Na2SiO3 solution using active Ca(OH)2 emulsion.NaOH was return to roast silicon residue through evaporating crystallization.The whole process realizes the comprehensive extraction of the valuable components in zinc oxide ore,and prepare ZnO,Fe2O3,SiO2,CaCO3,CaSiO3 products H2O and reaction medium of(NH4)2SO4 and NaOH were circularly utilized.The main conclusions are as follows:(1)The optimized reaction conditions of roasting zinc oxide ore using(NH4)2SO4 were concluded as below:material ratio of(NH4)2SO4 to zinc oxide ore of 1.4:1,roasting temperature of 475 ?,thermostatic time of 60 min.The factors in primary and secondary order influencing the zinc extraction ratio were material ratio,roasting temperature and thermostatic time.ZnCO3/ZnO reacted with(NH4)2SO4 to form(NH4)2Zn(SO4)2 firstly.Fe2O3 firstly reacted with(NH4)2SO4 to form(NH4)3Fe(SO4)3 and then generate(NH4)Fe(SO4)2.When the temperature was above 400 ?,Zn2SiO4 reacted with(NH4)2SO4 and its decomposition product to form(NH4)2Zn(SO4)2,and then decomposed into ZnSO4.The transformations from CaCO3 to CaSO4 and from PbO/PbCO3 to PbSO4 also took place.ZnSO4 and(NH4)2Zn(SO4)2 were soluble,so Zn joined into solution and separated from Si and Pb by water leaching.(2)There were four obvious endothermic peaks in each TG-DTA curve around 60 ?,200?,290 ? and 400 ?,respectively.The first one was assigned to eliminating moisture.The second one was attributed to the decomposition of(NH4)2SO4.The third one was attributed to the decomposition of(NH4)2SO4 and ZnCO3,the reactions between zinc compounds and iron oxides with(NH4)2SO4 and its decomposition products to generate(NH4)2Zn(SO4)2 and(NH4)3Fe(SO4)3.The fourth one was mainly ascribed to the reactions between Zn2SiO4 with(NH4)2SO4 and its decomposition products,the decomposition of(NH4)2Zn(SO4)2 into ZnSO4,the transformations from CaCO3 into CaSO4 and from PbCO3 to PbSO4 The reaction rate equations of the third peak and the fourth peak were as follows:d?/dt=Aexp(-e/RT)(1-?)n=4.89×104 exp(-103980/RT)(1-?)0.9676 d?/dt=Aexp(-E/RT)(1-?)n,=3.58×104 exp(-109070)(1-?)0.9166(3)The influences of reaction temperature,reaction time,pH value at reaction end and the initial concentration of Fe3+ on the removal ratio of iron were significant.The appropriate reaction conditions for making jarosite were concluded as follows:reaction temperature of 95?,reaction time of 3.5 h,pH value at reaction end of 3.0 at the initial concentration of Fe3+9.45 g'L"1.The concentration of residual Fe3+ in solution was lower than 0.3 g·L-1 after making jarosite.The physical aspect of(NH4)2Fe6(SO4)4(OH)12 was cluster figure composed of sheet or prismatic particles with smooth surface.The reaction temperature had significant influence on the removal ratio of Al,but the reaction time had no obvious effect.The appropriate reaction conditions were reaction temperature of 80 ?,reaction time of 10 min and pH value at reaction end of 5.4-5.6.The appropriate reaction conditions of(NH4)2Fe6(SO4)4(OH)12 hydrolysis were concluded as follows:hydrolysis temperature of 90 ?,hydrolysis time of 30 min,pH value of 12 at liquid-solid ratio of 4:1.The hydrolysis ratio was about 91%and high purity Fe2O3 with flower structure was obtained by drying and roasting the hydrolysis products.The appropriate carbonation conditions for NaAlO2 solution were carbonation temperature of 75 ? and pH value at carbonation end of 9.The obtained Al(OH)3 was fibre-like matter with loose structure and high purity.(4)The ZnO powders obtained by precipitation method were hexangularwurtzite structure with narrow size distribution.The preparation of Na2S by reducing Na2SO4 was discussed in the presence of catalyst.The appropriate reaction conditions using coal were material ratio of Na2SO4 to coal of 1:8,reaction temperature of 700 ?C and reaction time of 4h.The appropriate reaction conditions using CO were reaction temperature of 675 ?,reaction time of 2h and material thickness of no more than 4 cm,under which the conversion ratio was up to 95%.The appropriate reaction conditions using H2 were reaction temperature of 610 ?,reaction time of 1.5h and material thickness of no more than 4 cm,under which the conversion ration was about 95%.(5)The ZnO powders obtained by hydrothermal method were hexangularwurtzite structure.The molar ratio of OH-:Zn2+,reaction temperature and reaction time had significant influences on the micromorphologies of ZnO powders.Along with the molar ratio of OH-:Zn2+ and the temperature increasing,the flower-like structures of ZnO composed of flakes were more likely to grow into the flower-like structures of ZnO composed of needles and rods.However,if the molar ratio or the temperature was too high,the flower-like structures were broken down due to the growth of the rods.The appropriate reaction conditions for preparing flower-like structures were concluded as follows:molar ratio of OH-:Zn2+ of 5,reaction temperature of 150 ? and reaction time of 8h.The growth process of the ZnO powders with flake,rod and flower-like structures included the formation of Zn(OH)42-from Zn2+,the dehydration of Zn(OH)42-,the appearance of ZnO nuclei and the growth of ZnO crystals with different morphologies.(6)The appropriate reaction conditions of molten roasting silicon residue using NaOH were concluded as below:reaction temperature of 500 ? and reaction time of 90 min.The material ratio was variational due to the compositional variation.Na2SiO3 was firstly obtained when SiO2 reacted with NaOH,and then transformed Na4SiO4 along with the temperature increasing.Part of Na4SiO4 was turned into Na2CaSiO4.Lead compounds reacted with NaOH to form Na4PbO4 firstly and then generate Na6PbO5.Part of Na4PbO4 was turned into Ca2PbO4.Na4SiO4 was soluble,however Na2CaSiO4 was slightly soluble and Ca2PbO4 was insoluble,so the extraction ratios of Si and Pb were not high.(7)The pH value of solution at carbonation end was 8.5 under carbonation temperature of 80 ?,CO2 flow of 0.5 L·min-1 and stirring velocity of 400 r·min-1,under which the precipitation ratio of SiO2 was above 96%.The amorphous SiO2 particles were spherical with excellent thermostability.The indexes were up to the industry standard HG/T3061-2009.Under the stirring velocity of 400 r·min-1 and active calcium hydroxide emulsion of 168 g·L-1,the appropriate causticizing conditions were molar ratio of Ca(OH)2:Na2CO3 of 1.2:1,the concentration of Na2CO3 of 40-100 g·L-1,causticizing temperature 90 ?,causticizing time of 45 min.And under this condition the causticizing ratio was about 95%.When Na2SiO3 solution was causticized by the active calcium hydroxide emulsion,the regular and uniform CaSiO3 whisker was successfully synthesized using SDS and CTAB as dispersing agents.Employing SDS as dispersant,the appropriate conditions of synthesizing CaSiO3 whisker were as following:molar ratio of NaSiO3 to Ca(OH)2 of 1:1,reaction temperature of 220 ?,reaction time 9 h,mass fraction 10%SDS solution of 8-12 mL,Na2SiO3 solution of 0.05 mol·L-1.