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Research on Additive for Inhibiting Secondary Reaction in Clinker Leaching Process

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Tutor: BiShiWen
School: Northeastern University
Course: Non-ferrous metallurgy
Keywords: Sintered clinker,Secondary reaction,Alumina leaching rate,2CaO¡¤SiO2,Additive,Sod
CLC: TF821
Type: PhD thesis
Year:  2008
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Abstract:
There is 30% of 2CaO¡¤SiO2 in bauxite clinker which is produced by sintering method in alumina producing process.2CaO¡¤SiO2 can react with sodium aluminate in some conditions when clinker is leached.So some quantity of Al2O3 and Na2O that leached into solution from clinker will go into the red mud and it leads to loss of Al2O3.Thus the leaching ratio of Al2O3 was reduced,and the subsequent process and producing technique index were influenced as well.Based on the upon problems,this paper studied the additives to inhibit the secondary reaction of clinker. The alumina leaching ratio can be increased by adding additives during clinker leaching.This method can increase alumina output and improve producing technique index of some process without changing the original production process and equipments.what¡¯s more,the method is easy to operate, but it has great economic benefits.The additive that can improve 1% of alumina leaching ratio by inhibiting secondary reaction of clinker was screened and prepared preliminarily in the lab. Secondly, the impacts of the additive on the subsequent process------sedimentation of red mud and desilication of pregnant liquor were studied.Thirdly, the inhibiting mechanism was discussed.Fourthly, the adsorption behavior of additive adsorbed on 2CaO¡¤SiO2,distribution trend of solid-liquid separation and the accumulating speed of additive in sodium aluminate solution were investigated.The enlarged experiment and semi-industrial application experiment were carried out on the basis of lab experimentation.The main results were as follows:The decomposition of 2CaO¡¤SiO2 could be effectively inhibited by adding additive during clinker leaching.Sodium humate which was rich in aether, alcohol,and carboxyl was the most effective.The alumina leaching ratio was increased by 3.87% with 0.43% sodium humate added.But this quantity of additive was too high and could hardly apply industrially. Besides, sodium humate was brownish black in itself and it could darkle the product of aluminum hydroxide.So it couldn¡¯t be the final additive.Polymer AY1000 and PEG2000 had less inhibitory effect than sodium humate.The former which was rich in carboxyl could increase alumina leaching ratio by 2.17% with 0.10% additive and the latter of which could increase alumina leaching ratio by 1.48% with 0.25 % additive.The compound of polymer AY1000 and PEG2000 had synergistic effect,and the quantity of additive was reduced greatly.For example,DBDX which was compound of AY1000:PEG2000 equal to 1:1 could increase alumina leaching ratio by 1% with 0.003% additive.So DBDX met the requirements of production activity and it showed better economical benefits.Additive DBDX should be added in material-separating box of carbon denominator liquid and the solution that was dissolved with additive should be used up in 70 min, or it would be a failure.Polymer AY and PEG had the following effects on subsequent processes when the quantity that added was 0.05% weight ratio of clinker:they both speeded up sedimentation of the red mud,improved clarity of the overflow, and reduced liquid-solid ratio of the underflow. What was different was:polymer AY improved filtration property of the red mud while PEG worsened it.Compound additive DBDX could improve sedimentation of the red mud,clarity of the overflow and liquid-solid ratio of the underflow. What¡¯s more,it didn¡¯t affect filtration property of the red mud.The silica index of the second desilication that with additive AY or DBDX added during clinker leaching was not lower than that of without additive.So polymer AY and DBDX didn¡¯t have impacts on subsequent processes while used as additives.Infrared spectrometry of slag phase after sodium aluminate solution reaction was measured.SiO2 and Ca2+ concentrations were also analyzed. The results indicate that:the inhibition mechanism of polymer AY was adsorption on surface of¦Â-C2S by carboxyl,meanwhile the stable compounds was formed with Ca2+.The inhibition mechanism of polymer PEG was probably physical adsorption which is easy desorption.So the effect of PEG was lower than AY on inhibiting secondary reaction.Barium chloride method was established to determine polymer PEG in sodium aluminate solution.The optimal conditions for determining were:wavelength 520nm,iodine solution 3.0ml,BaCl2 1.0 ml and color-reacting time 2min. The liner regression equation that obtained under the optimal conditions was A= 0.2492+0.0836C.The linear relationship of the equation was good and it met the requirements of test accuracy.The adsorption that polymer AY and PEG adsorbed in the interface of dicalcium silicate-sodium aluminate solution was both saturated adsorption style. The time that AY and PEG adsorbed until saturated were 40min and 20min respectively. The adsorption that polymer AY adsorbed on dicalcium silicate particles was single molecule adsorption and the adsorption isotherm was "L" style,which was in accordance with Langmuin equation.The adsorption was mainly chemisorption and the adsorption free energy was EAY=57.89kJ/mol.The adsorption that polymer PEG adsorbed on dicalcium silicate particles was multimolecule adsorption and the adsorption isotherm was "S" style,which was in accordance with Freundlich equation.The adsorption was mainly physisorption and the adsorption free energy obtained from isotherm equation and empirical formula was EPEG=1.63kJ/mol and EPEG=2.44kJ/mol respectively.Almost 70% of DBDX was carried out by the red mud and 30% of it remained in sodium aluminate solution when 0.005% (weight ratio of clinker) of it added while leaching.So the accumulation of organic additive was not remarkable.The enlarged experiment was carried out in a 3L-volume ball mill.The place and method for adding additive were further investigated as well.The results showed that DBDX could inhibit secondary reaction of clinker and improve net leaching ratio of alumina more than 1%.The optimal method to add additive was:added the additive into sodium aluminate solution first and then leached the clinker with the solution in the mill.The industrial application experiment was carried out under the condition of alumina concentration 110¡«120g/L and the blanking speed in the boll mill 60t/h. Four boll mills were used in the experiment and one of them was added additive. The slurry after leaching went into corresponding separating tank respectively. The inhabitation effects of additive were evaluated by comparing the difference of the leaching ratio of alumina after first and second leaching between boll mills with and without additive.The results showed that leaching ratio of alumina with additive DBDX was improved to 1.12% than blank.It proved additive DBDX was available for inhibiting secondary reaction of clinker. Thus additive DBDX was exploited successfully.
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