Study On Electro-Conversion Process Of Pickled FeCl₃ Waste Solution In Steel Industry

The steel must be pickled before the rolling process to remove the oxide scale on the surface.At present,the pickling process is mainly hydrochloric acid pickling.However,during the pickling process of steel,a large amount of acidic waste solution containing FeCl3 will be generated.If it cannot be effectively treated,it will cause serious environmental pollution and even waste a lot of valuable components.At present,the most mature method for the treatment of hydrochloric acid pickling waste solution is the spray pyrolysis process,but this process has the disadvantages of high investment costs and harsh equipment operating conditions,and is especially not suitable for small-scale enterprise applications.Based on this,this paper proposes a new idea for low-cost clean treatment of valuable components.The new idea is diaphragm electrolytic conversion of iron-containing waste acid solution.This idea can make hydrochloric acid regeneration and iron recycling.In the new process of this paper,the basic problems in key steps such as the electrolytic conversion of iron hydroxide precipitation,recovery of hydrochloric acid and iron hydroxide calcined to prepare iron oxide powder are systematically studied.The main results are as follows:(1)Through thermodynamic calculations,this paper systematically study the equilibrium reaction equations and potential-pH relationships of related reactions in the Fe-H2O system,Mn-H2O system,and Zn-H2O system,and further draw the potential-pH diagram of Fe-H2O system,Mn-H2O system,and Zn-H2O system.The results of the potential-pH diagram of the Fe-H2O system show that the initial reaction temperature has a great effect on the pH value of the precipitate,and the iron ion concentration has no significant effect on the pH value of the precipitate.The cyclic voltammetry curves of the FeCl2 solution system and the FeCl3 solution system were tested respectively.The results show that iron is crystallized out as a precipitate during the electrolytic conversion process of the FeCl2 solution system and the FeCl3 solution system.However,FeCl3 system take place the reduction of Fe3+ to Fe2+ during the experiment,moreover the electrode reaction in the FeCl2 system experiment is reversible.(2)A single factor experiment was used to investigate the influence of factors such as current density,stirring rate,iron ion concentration,pole distance,NaCl concentration,initial reaction temperature,HCl concentration,and impurity ions on the electrolytic conversion process.The results show that for FeCl2 solution suitable conditions for the electrolytic conversion process of the system are:current density 3500 A/m2,stirring rate 300 r/min,initial reaction temperature 40?,Fe2+ concentration 125 g/L,pole distance 3.5 cm,NaCl concentration 3 mol/L,HCl concentration 0.4 mol/L.For FeCl3 solution system,the suitable electrolytic conversion process conditions are:current density 3500 A/m2,stirring rate 200 r/min,initial reaction temperature 30?,pole distance 3.5 cm,NaCl concentration 3 mol/L,and HCl concentration 0.4 mol/L.The low-concentration impurity ions Mn2+ and Zn2+ have no significant effect on the electrolytic conversion process of FeCl2 and FeCl3 systems.(3)The precipitates obtained from the electrolytic conversion of FeCl2 and FeCl3 systems were respectively studied by calcination experiments,and the influence of calcination temperature was investigated.The results show that the calcined precipitation products obtained from the electrolytic conversion of the two systems are all calcined ?-Fe2O3;the suitable calcination temperature of the FeCl2 system electrolytic conversion precipitation product is 500?,and the suitable calcination temperature of the FeCl3 system electrolytic conversion precipitation product is 600?.The calcined product is nano-iron oxide particles with relatively uniform distribution.