Investigating Effects Of Phosphogypsum Disposal Ways On The Environment And Economic Performance Of The Phosphate Fertilizer Production Integration System

Phosphogypsum,as the main by-product of phosphate fertilizer production,has a large amount of production and a low comprehensive utilization rate,which is easy to cause resource waste and environmental pollution.It has become one of the important factors restricting the sustainable development of the phosphorus chemical industry.The stockpiling of large quantities of phosphogypsum not only takes up valuable land resources but also leads to serious water and soil pollution,especially chemical and radioactive pollution.Therefore,it is urgent to reduce the environmental degradation caused by phosphogypsum disposal.With the implementation of a series of policy measures such as’three phosphorus’remediation,the comprehensive utilization level of phosphogypsum in China has been significantly improved.However,the process of resource utilization of phosphogypsum is inevitably accompanied by additional investment in resources and energy sources.Furthermore,it may also generate new environmental impacts that require additional resources and labor to eliminate.Therefore,it is necessary to quantitatively assess the advantages and disadvantages arising from different phosphogypsum disposal methods.To investigate the impact of the utilization of phosphogypsum resources on the comprehensive performance of phosphorus fertilizer production,the environmental and economic performance of different phosphogypsum disposal methods was analyzed based on emergy value theory and quantification of pollutant emissions,combined with carbon emissions accounting and economic analysis methods.Finally,the Synergy Effect Index（SEI）was proposed to comprehensively evaluate the synergistic effect between the environmental performance and economic benefits of different schemes.A monoammonium phosphate production enterprise in Yichang City,as an example,is investigated using the proposed methodology and indicators by considering its four scenarios,including S1:phosphate fertilizer production subsystem+phosphogypsum storage subsystem,S2:phosphate fertilizer production subsystem+phosphogypsum manufacturing building materials subsystem,S3:phosphate fertilizer production subsystem+phosphogypsum manufacturing fertilizer filling materials subsystem,and S4:phosphate fertilizer production subsystem+phosphogypsum manufacturing cement retarder subsystem.These scenarios were analyzed and compared to find the optimal phosphogypsum disposal method.The main research results are summarized as follows:（1）According to the emergy flow analysis,the emergy input of S1,S2,S3,and S4 is1.11E+21 sej/yr,1.14E+21 sej/yr,3.40E+21 sej/yr and 1.19E+21 sej/yr respectively.The proportion of purchased non-renewable emergy is the largest（80.45～99.71%）in either a single subsystem or the overall system.In terms of the contribution of the different input items,the main contributors to the total emergy are mainly phosphate rock,liquid ammonia,and Fertilizer-grade dicalcium phosphate.Compared with S1,the other three scenarios all enhance the emergy input to varying degrees（3.07～206.36%）,among which S3 raises the emergy input the most,mainly from the increased input of fertilizer-grade dicalcium phosphate and phosphate tailings.（2）The results of the quantitative analysis of the pollutant emissions’impact show that the total emergy value of pollutant emissions’impact is 1.03E+19 sej/yr,6.84E+18 sej/yr,6.83E+18 sej/yr,and 6.80E+18 sej/yr for S1,S2,S3,and S4,respectively.They are mainly from ecological services（51.99%,69.16%,69.21%,and 69.57%）,which are mainly used to dilute the total phosphorus in wastewater and dust in the exhaust gas.In terms of emergy loss,it is mainly caused by dust,fluorinated gas,and SO₂ in waste gas.Compared with S1,phosphogypsum reuse reduces the impact of pollution emissions to varying degrees（33.87～34.25%）,mainly due to the dust generated by the weathering of phosphogypsum and the discharge of leachate from the slag yard were avoided.（3）According to emergy indicators,the EYR index value showed the superiority of S2（10.33E-01）,followed by S1（10.28E-01）,S4（10.27E-01）,and S3（10.09E-01）.The ELR index values follow the trend of S3（9.25E+00）<S2（2.71E+01）<S1（3.16E+01）<S4（3.37E+01）.In terms of ESI,S3 has the highest sustainability level（1.09E-01）,followed by S2（3.82E-02）,S1（3.25E-02）,and S4（3.04E-02）.S3 performed best in terms of pollutant emission intensity（7.18E+13 sej/ten thousand yuan）,followed by S2（3.66E+14 sej/ten thousand yuan）and S4（4.03E+14 sej/ten thousand yuan）,while S1 had the highest pollutant emission intensity（7.10E+14 sej/ten thousand yuan）.Therefore,S3 has the highest level of environmental sustainability among the four scenarios,but in the long run,the four scenarios are not sustainable.（4）According to the carbon emission accounting,compared with S1,the total carbon emissions of S2,S3,and S4 increased by 64.64%,2.40%,and 1.02%respectively.Their main sources of carbon emissions are the combustion of fossil fuels（such as coal,and natural gas）and the release of CO₂ from the decomposition of phosphate rock in the production process.As far as the carbon emission per unit profit is concerned,compared with S1,the carbon emission intensity of S3 and S4 decreases by 84.33%and 12.86%respectively,while that of S2 increases by 28.44%.S2 has the highest carbon emission intensity.This is mainly due to its rapidly increasing power consumption and fossil fuel input.（5）The results of the economic analysis show that the four scenarios all have economic feasibility.The economic benefit of the phosphogypsum resource utilization scenario is better than that of the phosphogypsum storage scenario.Among them,S3 has the highest economic benefit cost ratio（EBCR,2.61E+00）and the strongest profitability,followed by S2（1.41E+00）and S4（1.38E+00）.（6）According to the synergistic benefit index,the SEI value of the phosphogypsum storage scenario S1 is 2.22E-01,and the SEI values of the phosphogypsum resource utilization scenarios（S2,S3,and S4）are 4.16E-01,9.17E+01 and 4.34E-01,respectively.It can be seen that the resource reuse of phosphogypsum can improve the comprehensive performance of phosphate fertilizer production.The SEI value of S3 is much higher than that of other scenarios,and it has the best comprehensive performance.Based on the above conclusion,this study proposes the following suggestions,including（1）improving the energy mix for cutting carbon emissions,（2）optimizing the production process for reducing operating costs,（3）strengthening pollutant emissions control,and（4）emphasizing life cycle management of phosphogypsum.