Study On The Effect Of Solution Supersaturation On The Synthesis Of Scorodite Under Normal Pressure System

The non-ferrous metal industry is one of the main sources of arsenic pollutants.Therefore,the safe disposal of arsenic-containing materials is an urgent problem for the non-ferrous metal industry.Scorodite has the characteristics of high arsenic content,stable chemical properties,and low storage cost.It is considered to be the best carrier for arsenic fixation.The stable solidification of arsenic in the form of scorodite has a significant impact on the sustainable development of the nonferrous metallurgical industry.The synthesis of crystalline scorodite is the basis for the safe disposal of arsenic in the form of scorodite.Stability is the key.It is the development direction to further reduce the supersaturation of the solution to achieve the large-scale and high-stability scorodite synthesis.The supersaturation in the scorodite synthesis system is the key factor affecting the particle size and stability,and has a great effect on the crystalline structure and stability of scorodite.Existing hydrothermal synthesis methods,atmospheric pressure methods,and ferrous ion oxidation methods rarely involve the effect of oversaturation on the process of scorodite.Therefore,this article focuses on the thermodynamics of the Fe-As-H₂O system and the supersaturation of Fe???-As?V?-H₂O and Fe???-As?V?-H₂O systems on the size and stability of scorodite particles.And the kinetics of ferrous oxidation in the Fe???-As?V?-H₂O system in order to synthesize crystalline scorodite with large size and high stability.The main research contents and conclusions are as follows:?1?Potential p H diagrams of Fe-As-H₂O series at 65°C and 90°C atmospheric pressure were plotted,and the theoretical stable existence areas of iron arsenate at 65°C and 90°C were 0.017<p H<4.9 and-0.305<p H<5.224.Scorodite synthesis needs to be carried out under acidic conditions.At 90°C,its stable p H range is-0.305 to 5.224.Increasing the temperature is beneficial to scorodite synthesis.?2?The effects of initial supersaturation with and without seed crystals on Fe???-As?V?system on arsenic-iron precipitation rate,scorodite component content and stability were studied.The results show that the scorodite synthesized without seed crystals has poor stability and low arsenic-iron precipitation rates,and the arsenic-iron rates are between 19.68%?41.31%and 24.4%?40.41%,respectively.Between 4 and12.5 mg/L,only when the initial supersaturation was 151.2,the leaching arsenic concentration of scorodite reached 4 mg/L,which meets the requirements of the national standard of 5mg/L.The scorodite synthesized under the condition of seeding has high stability and high arsenic precipitation rate,and its arsenic and iron rates are33.72%?76.84%,24.06%?54.61%,and its leaching arsenic concentration is between0.7?1.9 mg/L,All reach the national standard 5mg/L.?3?The effects of initial p H,initial arsenic concentration,and reaction temperature on supersaturation and the initial supersaturation on arsenic-iron precipitation rate,scorodite component content,morphology,particles size and stability in the Fe???-As?V?system were studied.The results show that the supersaturation of the solution can be effectively controlled by controlling the initial p H,the initial arsenic concentration,and the reaction temperature.Properly reducing the initial p H and arsenic concentration can control the lower solution supersaturation,which is conducive to the growth of crystal particles to prepare large scorodite.Properly increasing the reaction temperature can increase the supersaturation of the solution,which is conducive to the formation of high crystalline Stinky stone.Properly increasing the initial supersaturation is conducive to increasing the precipitation rate of arsenic and iron,as well as synthesizing crystalline and high-stability spherical large particles of scorodite,but it has little effect on the content of arsenite and iron.When the initial supersaturation is 41.74,the arsenic-iron precipitation rate is 81.98%,58.63%,the particle size is 58.3-87.5?m,the arsenic-iron content is 30%,24%,and spherical crystalline scorodite with leaching arsenic concentration of 0.64mg/L?4?The effects of initial p H,reaction temperature,and initial arsenic concentration on the oxidation rate of ferrous iron and the relationship between the oxidation rate of ferrous iron and the degree of supersaturation were studied under atmospheric pressure Fe???-As?V?system.The results show that properly reducing the initial p H and reaction temperature of the solution can reduce the ferrous salt oxidation rate to reduce the supersaturation of the solution,and the reduction of the initial arsenic concentration can increase the ferrous oxidation rate.The degree of supersaturation increases with the increase of the ferrous oxidation rate.When the ferrous oxidation rate is 0.00237,it is beneficial to synthesize large particles and highly stable crystalline spherical scorodite particles.