RESOURCE REUTILIZATION FOR PHOSPHOGYPSUM AND RED MUD THOUGH CO-TREATMENT
Phosphogypsum(PG)and red mud(RM)are two kinds of solid residue.Up to date,however,the approach to efficient utilization for the two residues faces technical difficulties due to their large emissions,complex composition,and high environmental risk.Based on the mineral characteristics that PG is a basic waste with high calcium,and RM is an acid residue with high alumina and silica,we proposed an innovative approach to recycle calcium and recover aluminum and sodium simultaneously by con-treating the two residues at high temperatures.The results of the laboratory-scale test showed that the optimum parameters for co-processing of PG and RM were sintering temperature 850 ℃,twice stoichiometric amount of reductant,n(CaO)/n(SiO2)=2.1,n(Na2O)/n(Al2O3)=1.1,and sintering time of 7 minutes.Under these conditions,the recovery rates of aluminum and sodium were 82.14%and 83.48%,respectively.Moreover,the pilot test was carried out under this condition.The results showed that the recovery rates of aluminum and sodium were slightly lower(76.32%for Al2O3,and 81.25%for Na2O)than those of the laboratory-scale test;XRD analysis of the sintered sample and its corresponding leached residue showed that the peak value of Na/Al-bearing materials was weakened,while the diffraction peaks of Ca-Si compounds in the residue became stronger compared with the sintered sample,indicating that the sodium aluminate in the sintered product was effectively dissolved,and the insoluble Ca-Si materials were enriched in the residue.Furthermore,the morphology of the two samples was observed by SEM,the sintered product presented large agglomerated particles with loose structure,while most of the large agglomerate disappeared in the leached residue,indicating that soluble Na-and Al-bearing compounds were dissolved out,which agreed well with the observed XRD results.Moreover,the sodium aluminate solution obtained by the leaching process was treated by the carbonation decomposition to produce Al(OH)3.Compared to the Al(OH)3 supplied by a large aluminum plant in Guizhou,the two products both contain similar Al2O3 content,but the former was with higher impurity content present,which may be due to the differences between the raw materials and processes.The results show that the novel idea for resource re-utilization of phosphogypsum and red mud through a co-treatment process is feasible.However,the leached residue is difficult for further utilization due to its high alkali content(approximately 3.19%Na2O).Therefore,this technology still needs to be optimized for a high-purity refined Al(OH)3 product and leached residue with a low alkali content.
phosphogypsumred mudcon-treatmentresource utilizationpilot test