Study On Removal Of SO₂ From Nonferrous Smelting Flue Gas By Smelting Dust Slurry

SO₂ emissions of non-electric industries mainly from the metallurgy and chemical industry are very large.Most of the traditional wet desulfurization technology is used to purify sulfur dioxide,in particular the limestone gypsum method.However,with the improvement of environmental protection standards and the progress of purification technology,the traditional limestone gypsum method is not suitable for the purification of SO₂ in the non-ferrous smelting industry,because the flue gas of non-ferrous smelting contains heavy metals.Thus,the desulphurization gypsum contains heavy metals and generates a new hazardous waste,which produces secondary pollution and brings new environmental protection problems.Aiming at the low concentration SO₂ in the flue gas of non-ferrous metal smelting,this paper selects the soots as the novel desulfurization agent,which is produced directly from the non-ferrous metal smelting industry.The chemical composition and phase structure of two kinds of soot(manganese smelting dust and closed calcium carbide furnace ash)were analyzed.After the preparation of the slurry,the SO₂ removal efficiency was studied,including the influence of different process parameters on the desulfurization efficiency.The purpose of this paper is to provide a new idea for solving the problems of flue gas desulfurization and solid waste disposal in non-ferrous industries through the development of the smelting slag slurry method.The main conclusions of the study are as follows:(1)The phase structure and chemical composition of manganese smelting dust was investigated.It was found that the phase structure of manganese smelting dust consisted of metal oxide and silicate minerals,which has the feasibility of desulphurization.Furthermore,the effects of the reaction conditions on the desulfurization efficiency by manganese smelting dust slurry were investigated.Through the optimization of preparation of manganese smelting dust slurry(manganese smelting dust slurry concentration of 4 g/L),the next experiments were carried out at the condition of the gas flow rate of 800 m L/min and inlet SO₂concentration of 4570 mg/m³.The effects of oxygen content,p H value of initial slurry,reaction temperature,and stirring rate on desulfurization efficiency were investigated in detail by single-factor experiments.The optimal experimental conditions were stated as follows:(1)oxygen content of 10%;(2)p H value of initial slurry of 11.7±0.3;(3)reaction temperature of slurry of 35?;(4)stirring rate of slurry of 2500 r/min.Under optimal conditions,manganese smelting dust slurry obtained the penetration time of 420 min.(2)The phase structure of closed calcium carbide furnace ash was investigated,the results showed that the Fe and Zn metal oxides and alkaline oxides are contained in ash,which can replace traditional limestone as a new desulfurization agent.The best slurry preparation condition for closed calcium carbide furnace ash was determined at a slurry concentration of 4 g/L.When the gas flow rate is 800 m L/min,the inlet SO₂ concentration is 5140 mg/m³,effects of oxygen content,p H value of initial slurry,reaction temperature,and stirring rate on desulfurization efficiency were investigated by single-factor experiment.The optimal experimental conditions were stated as follows:(1)oxygen content of 15%;(2)p H value of initial slurry of 10.8±0.5;(3)reaction temperature of slurry of 35?;(4)stirring rate of slurry of 2500 r/min.Under optimal conditions,990 min penetration time of closed calcium carbide furnace ash slurry was obtained.(3)Comparing the two kinds of soot as desulfurization agents,it is found that the SO₂ outlet concentration of closed calcium carbide furnace ash slurry can meet the emission limit of 35 mg/m³ during a reaction time of 990 min under the optimal process parameters.Compared with manganese smelting dust slurry,the maintenance time surpasses 570 min.This may be due to the presence of the higher content in iron/zinc metal oxides in the closed calcium carbide furnace ash than manganese smelting dust.The leached iron and zinc ions during the reaction have the ability of liquid-phase catalytic oxidation for sulfur dioxide,thus leading to a faster removal rate and higher sulfur capacity.But the electric furnace ash slurry depends on the higher oxygen content.From the observation of sulfur dioxide penetration time,it is concluded that the closed calcium carbide furnace ash slurry has a better desulfurization effect and can be used in expanded desulfurization tests.