Study On The Separation Of Ca²⁺,Mg²⁺,Fe³⁺,Al³⁺ Ions From The Phosphoric Acid-nitric Acid Solution Using Ion Exchange Resin

The phosphoric acid-nitric acid solution is the neutralization mother liquor obtained by using nitric acid resolve phosphate ore,which can be used to produce nitrogen and phosphorus compound fertilizer.In addition to phosphoric acid(4.4 mol·L^-1)and nitric acid(1.1 mol·L^-1),this solution also contains a lot of Ca²⁺ion(1.9 mol·L^-1)and a few Mg²⁺,Fe³⁺,Al³⁺ions(0.14?0.24 mol·L^-1).During the neutralization process,the presence of these metal ions leads to the formation of a large amount of precipitates in the phosphoric acid-nitric acid solution,which makes slurry easily viscous and water-soluble phosphorus degenerate.In order to alleviate such problems,precipitation method is usually used to remove the most of Ca²⁺ion from the phosphoric acid-nitric acid solution in industry.But limited by the solubility of metal ions,the small amount of Ca²⁺,Mg²⁺,Fe³⁺,Al³⁺ions still remain in the solution.For this purpose,the dissertation firstly studies the influence rule of Ca²⁺,Mg²⁺,Fe³⁺,Al³⁺ions on the neutralization process of the phosphoric acid-nitric acid solution,which can lay a foundation and provide a direction for the separation of these metal ions.Secondly,taking advantage of ion exchange resin as adsorbents,this thesis focuses on the advanced separation process of Ca²⁺,Mg²⁺,Fe³⁺,Al³⁺ions from the phosphoric acid-nitric acid solution.The primary research contents are as follows:(1)For the issues that slurry is easy to become viscous and water-soluble phosphate degenerates in neutralization process,according to the constituents of neutralization mother liquor,the phosphoric acid-nitric acid solutions with unitary,binary,and quaternary metal ions were designed and used to investigate the influence of metal ions on the slurry rheological behavior and the generated water insolubles in neutralization process with ammonia gas.The results reveal that when the phosphoric acid-nitric acid solution contains 0.05?0.25 mol·L^-1single Mg²⁺ion,Fe³⁺ion,Al³⁺ion or 0.05?2.0 mol·L^-1 single Ca²⁺ion,the slurry displays great rheological behavior,but water-insoluble phosphate and ammonium are generated in the solution at the end of neutralization process.As for the phosphoric acid-nitric acid solution with 2.0 mol·L^-1 Ca²⁺ion,when it coexists with 0.05 mol·L^-1 Mg²⁺ion,the slurry rheological behavior is almost unchanged,but when it coexists with 0.05 mol·L^-1 Fe³⁺ion or Al³⁺ion,the more NH₄⁺and NO₃^-ions in solution transform into precipitates and the slurry rheological behavior gets worse.For the quaternary metal ions phosphoric acid-nitric acid solution(the concentrations of Mg²⁺,Fe³⁺,and Al³⁺ions are 0.25mol·L^-1,respectively),when Ca²⁺ion concentration is in 0.25?0.5 mol·L^-1,the slurry exhibits fine rheological behavior,but when Ca²⁺ion concentration is 1.0mol·L^-1,a large amount of PO₄^3-,NH₄⁺,and NO₃^-ions in solution(3.43,4.26,2.24 mmol·g^-1)form precipitates,the slurry rheological behavior worsens severely,and the neutralization process cannot be completed smoothly.Thus,in order to avoid slurry becoming viscous in neutralization process,it is indispensable to remove a lot of Ca²⁺ion from the phosphoric acid-nitric acid solution;in order to avoid water-soluble nitrogen and phosphorus degeneration,it is necessary to remove completely a few Ca²⁺,Mg²⁺,Fe³⁺,Al³⁺ions from the phosphoric acid-nitric acid solution.(2)For the purpose of removing completely Ca²⁺,Mg²⁺,Fe³⁺,Al³⁺ions from the phosphoric acid-nitric acid solution,using 001×7 resin as adsorbent,batch adsorption process and dynamic adsorption and elution process were investigated to explore the feasibility of separating Ca²⁺,Mg²⁺,Fe³⁺,Al³⁺ions by this resin and optimize operating parameters.Finally,FT-IR and XPS characterizations were carried out to understand purification mechanism of resin.The results suggest that 001×7 resin presents better adsorption ability to Ca²⁺and Mg²⁺ions(0.80 and 0.66 mmol·g^-1)in the phosphoric acid-nitric acid solution while worse adsorption performance to Fe³⁺and Al³⁺ions(0.02 and0.20 mmol·g^-1).001×7 resin is capable of removing effectively the coexistent Ca²⁺and Mg²⁺ions from the phosphoric acid-nitric acid solution,and the separation process has a great cycling stability.The optimum operational parameters are the up flow mode,1.0 m L·min^-1 feed flow rate,0.25 mol·L^-1initial ion concentration,45 cm column height,and 7 mol·L^-1 nitric acid regeneration solution.The purification mechanism of resin is based on the reversible ion exchange reaction between sulfonic acid group on resin and Ca²⁺,Mg²⁺ions,thereby realizing the recyclability of separation process.Therefore,the separation process using 001×7 resin to remove completely Ca²⁺and Mg²⁺ions from the phosphoric acid-nitric acid solution exhibits a good application prospect.(3)In order to screen out the applicable resin for the sparation of Fe³⁺and Al³⁺ions from the phosphoric acid-nitric acid solution,using S957,S950,S930resins as adsorbents,batch adsorption process and dynamic adsorption and elution process were studied to explore the adsorption and elution performance of different resins to Fe³⁺and Al³⁺ions.The results indicate that both S957 resin and S950 resin present better adsorption ability to Fe³⁺and Al³⁺ions in the phosphoric acid-nitric acid solution(0.76,0.40 mmol·g^-1 and 1.04,0.80mmol·g^-1).S957 resin shows a stable adsorption and elution ability to Fe³⁺and Al³⁺ions in the adsorption-elution process with seven times,but S950 resin expresses bad regeneration performance.S957 resin is able to remove selectively Fe³⁺and Al³⁺ions from the phosphoric acid-nitric acid solution with Ca²⁺,Mg²⁺,Fe³⁺,Al³⁺ions,and has less adsorption ability towards Ca²⁺and Mg²⁺ions.Consequently,S957 resin is the optimal adsorbent,which can be used to remove completely Fe³⁺and Al³⁺ions from the phosphoric acid-nitric acid solution.(4)In order to study intensively the separation process of Fe³⁺and Al³⁺ions from the phosphoric acid-nitric acid solution,using S957 resin as adsorbent,adsorption kinetics,dynamic adsorption and elution process of Fe³⁺and Al³⁺ions were investigated and the operational parameters were optimized.Finally,BET,FT-IR and XPS characterizations and quantum chemistry computation were carried out to explore purification mechanism of resin and the bonding mechanism between functional groups on resin and metal ions.The results demonstrate that phosphoric acid has the significant inhibiting effect on the adsorption rates of Fe³⁺and Al³⁺ions on S957 resin.Their adsorption equilibriums are reached at 60 and 40 min reaction times,respectively.The optimum dynamic operational parameters are 0.5 m L·min^-1 feed flow rate and 8mol·L^-1 hydrochloric acid regeneration solution.The purification mechanism of S957 resin is based on the ion exchange reaction between phosphonic acid group and Fe³⁺and Al³⁺ions,while porous structural parameters and sulfonic acid group have little influence.Owing to the larger binding energy of phosphonic acid group with Fe³⁺and Al³⁺ions,S957 resin still present great adsorption performance to Fe³⁺and Al³⁺ions in the phosphoric acid-nitric acid solution under the influence of dihydrogen phosphate ion.Hence,the separation process using S957 resin has a good application prospect in the complete removal of Fe³⁺and Al³⁺ions from the phosphoric acid-nitric acid solution.