Study On Preparation Of Calcium Aluminate Cement Raw Material From Aluminum Processing Sludge

China is a big country in processing and manufacturing aluminum profiles,accounting for more than 50%of the global aluminum profile production,and it is also a major consumer of aluminum profiles.In order to improve corrosion resistance and wear resistance of aluminum profile products,surface treatments such as degreasing,polishing,acid etching,alkali etching,ash removal,anodizing,coloring,sealing and spraying,etc are required.Large amount of sewage are generated during these process.The sewage is then processed by precipitation,flocculation,and filter press to obtain aluminum processing sludge.Currently the annual output of aluminum profiles is about 20 million tons,and the comprehensive wastewater sludge is about 2 million tons.Each year large amount of processed sludge is produced.If these by-products are misused and disposed inappropriately,it will have a negative impact on the environment.Due to the level of aluminum content in the sludge,28%to 38%,the sludge is huge can be used as a substitute for high-aluminum raw materials.The purpose of paper is to solve the problems of aluminum processing sludge,which is difficult to absorb due to its huge annual output and difficult to industrialize its composition.It is prepared into calcium aluminate cement raw materials due to its large annual output and high aluminum raw material consumption.This type of industry has the ability to absorb a large amount of aluminum processing sludge,and can also make full use of the high aluminum content of aluminum processing sludge.First,the aluminum processing sludge of six different manufacturers was investigated and the total element analysis was carried out.Combined with the maximum limit of the relevant chemical elements of calcium aluminate cement products in GB/T201-2015"Aluminate Cement"（sulfur≤0.2%,Chlorine≤0.06%,Alkali≤0.5%,Iron oxide≤3%,Silica≤9%）,it is found that if the sludge is used as the raw material of calcium aluminate cement,the sulfur,chlorine,and alkali obviously exceed the standard,so impurity removal is required to deal with.In order to further carry out the research work,this paper takes the sludge of one of the manufacturers as the research object.In order to have a preliminary understanding of the overall physical and chemical properties of the sludge,the sulfur,chlorine,and alkali（sodium,potassium）contained in the sludge are quantified using analysis method,XRD,SEM and thermogravimetric analysis.The results showed that the sludge contained 2.54%sulfur,0.1%chlorine,and 4.62%alkali.XRD analysis results show that the aluminum in the sludge mainly exists in the form of Al（OH）₃ and Al OOH（boehmite）,and the sulfur mainly exists in the form of Ca SO₄（H₂O）_0.5（hemihydrate gypsum）.Scanning electron microscopy（SEM）results show that the sludge is composed of many small particles,the size of which is 2-3μm,and the surface of the sludge is loose and porous.The results of thermogravimetric analysis showed that the sludge lost 35.2%from room temperature to 850℃.There are two obvious endothermic peaks on the DCS curve at this stage,located at 113℃and 304°C,indicating that the sludge dewatering is staged.In order to solve the problem of high sulfur content in sludge,this paper adopts roasting reduction method to desulfurize,first reduce the high-valence sulfur in the sludge to low-valence sulfur and then remove it from the sludge.In the experiment,the reducing agent is firstly screened,and finally the reducing agent is preferably carbon powder.It is calculated by thermodynamics that carbon powder can reduce the thermal decomposition temperature of calcium sulfate effectively.The experimental results show that:when the roasting temperature is 900℃,the mass ratio of carbon powder to sludge is 0.16,and the roasting time is 50 min,the desulfurization rate of the sludge reaches 92.6%,and the sludge contains 0.19%sulfur at this time.In order to solve the problem of high chlorine and alkali（sodium,potassium）content in sludge,this article uses deionized water elution method to remove chlorine and alkali,mainly using the solubility of chlorine,sodium,and potassium in the sludge.The experiment first screened the elution method,and the final preferred elution method was ultrasonic assisted elution.The experimental results show that the best dechlorination process is the elution temperature is 45℃,the liquid-solid ratio is 20ml/g,the ultrasonic time is 5min,the elution rate of chlorine in the sludge is 49%,and the chlorine content is 0.051%.The best alkali removal process is as follows:the mass ratio of calcium oxide to sludge is 0.075,the elution temperature is 70℃,the liquid-solid ratio is 20ml/g,the ultrasonic time is 15min,the elution rate of alkali in the sludge reaches 80.09%,and the alkali content is 0.46%.