Optimization Of Neutralization Process Of The Acidic Wastewater In Titanium Dioxide Production Using Sulfuric Acid

Large quantities of acidic wastewater are produced in titanium dioxide production using sulfuric acid.How to effectively treat the acidic wastewater is an important problem,which attracts extensive attention in the titanium dioxide industry.Traditional neutralization process with calcium oxide(CaO)exist some problems: great consumption of CaO,low CaO reaction efficiency,poor press filtration performance of the by-product gypsum and so on.In order to effectively solve these problems,some relative researches had been done in this paper.In this paper,slaking conditions were discussed firstly and correspondingly created favorable conditions for reducing Ca O consumption and improving CaO reaction ratio.Under the experimental conditions of this paper,the best slaking parameters were: mass ratio between H2 O and CaO,4:1;stirring speed,300r/min;initial water temperature,35℃;particle size of CaO,below 0.075 mm.An advantageous neutralization effect was achieved when using Ca(OH)2,which was produced under the best slaking conditions.The effect of neutralization conditions on crystal growth and filtration performance of gypsum were also investigated in this paper.The optimal conditions which were favorable for the press filtration of gypsum sludge were: 2% of the concentration of Ca(OH)2,5m L/min of the addition rate of Ca(OH)2,45℃-55℃ of reaction temperature.There was no significant change in filtration rate under various agitation intensity and agitation time.However,crystal morphology had obvious effect on the performance of press filtration.Furthermore,the impacts of mental ions on crystal growth and filtration performance of gypsum were discussed.The results showed that,the addition of Al3+,Mn2+,Mg2+ had negative impacts on the filtration performance of gypsum.The filtration rate was decreased when a little or a large amount of Fe2+ was added into the reaction system.However,the filtration rate was improved when the content of FeSO4 was in the range of 0.8%-1.8%.Finally,based on the above research,the calcium sulfate produced in the system was used as seed crystals,and gypsum sludge recycle method was applied into the treatment process of the acidic wastewater from titanium dioxide production.A treating process of “CaCO3 – CaO two stages neutralization-flocculation – sludge recycle” was created in this paper.The parameters including the final pH value of CaCO3,type and dosage of flocculant,concentration of the recycled sludge,dosage of the recycled sludge,recycle time were respectively found to be: pH=5.5;0.6mL CPAM(0.1%)when treating 1L wastewater;inicial concentration of the treated sludge before press filtration;500mL recycled sludge when treating 1L wastewater;recycle 3 times.Compared to the traditional treating process,the process of “CaCO3 – CaO two stages neutralization-flocculation – sludge recycle” raised the filtration rate from 24.63% to 63.77% and saved about 14.75 kg CaO when treating 1m3 wastewater.What’s more,it could save about 468.89 t lime(including 85% CaO)for a factory per day when the daily yield of titanium dixode was considered to be 200 t.The process of “CaCO3 – CaO two stages neutralization-flocculation – sludge recycle” was proved to effectively decreased the consumption of CaO,significantly improved CaO reaction efficiency and press filtration performance of by-product gypsum.