In the production of magnesium castings, the realization of environmental protection requirements needs to run through the entire process of smelting, casting, and post-processing, and smelting flue gas treatment is a key link. The following is an explanation from two aspects: environmental protection measures system and flue gas treatment technology:
一. Environmental protection measures for the entire process of magnesium casting production
1. Smelting link: source pollution control and energy optimization
Low-pollution smelting technology
Use inert gas protection smelting (such as CO₂, SF₆ mixed gas) to replace traditional fluoride salt flux and reduce the emission of toxic gases such as hydrogen fluoride (HF) and chlorine (Cl₂). For example, a German factory uses CO₂+0.1% SF₆ protection, and the fluoride concentration in the flue gas is reduced from 50mg/m³ to below 5mg/m³ (EU emission standard is 10mg/m³).
Promote the use of electric induction melting furnaces to replace oil furnaces, increase the power conversion rate to 85% (oil furnaces are about 60%), and reduce NOx emissions by 40%-60%.
Waste recovery and energy consumption control
Establish a closed circulation system to process magnesium chips, gate materials and other waste materials through crushing-screening-remelting, with a recovery rate of more than 95%. A domestic enterprise reduces solid waste emissions by 2,000 tons and energy consumption by 12% each year through direct waste remelting technology.
2. Casting and post-processing: process innovation to reduce pollution
Less/no cutting process
High-pressure die casting achieves near-net forming of magnesium castings (dimensional tolerance ±0.1mm), reduces machining processes, reduces cutting fluid usage by 70%, and reduces waste generation by 50%.
Green surface treatment
Use chromium-free passivation (such as silane treatment, rare earth conversion film) instead of hexavalent chromium electroplating, and wastewater COD (chemical oxygen demand) is reduced from 500mg/L to below 100mg/L. For example, a new energy vehicle battery shell uses silane coating, which has a salt spray test of 1,000 hours without corrosion, and reduces wastewater treatment costs by 30%.
3. Comprehensive waste management
Wastewater treatment
Establish a three-level treatment system: regulating tank (neutralizing pH value) → chemical precipitation (removing heavy metal ions) → membrane filtration (COD removal rate 90%), the effluent can be reused in the cooling system, and the water reuse rate reaches 85%.
Classification and disposal of solid waste
After the smelting slag is magnetically separated to recover magnesium metal, the remaining slag is used to produce refractory materials; the waste release agent is regenerated by distillation, and the recovery rate reaches 80%.
二. Core technology for magnesium smelting flue gas treatment
1. Flue gas composition and characteristics
Main pollutants: MgO dust (accounting for 60%-70%), fluoride (HF, MgF₂), trace metal vapor (such as Zn, Pb) and organic volatiles (decomposition products of release agent).
Flue gas characteristics: high temperature (300-500℃), fine dust particle size (0.1-10μm), and highly corrosive fluoride.
2. Mainstream treatment technologies and process combinations
(1) Dry purification technology
Bag dust removal + activated carbon adsorption
Principle: The flue gas is first cooled to 120-150℃ by the waste heat boiler, then passed through a bag dust collector (filter bag material is PTFE, filtration efficiency ≥99.9%) to remove MgO dust, and finally through an activated carbon adsorption tower to remove fluoride and organic pollutants.
Case: A magnesium alloy wheel hub factory adopts this process, and the dust emission concentration is <10mg/m³, and the fluoride is <1mg/m³, which meets the special emission limit values of China's "Industrial Furnace Air Pollutant Emission Standard" (GB 9078-1996).
Electrostatic precipitator + dry defluorination
Principle: The electrostatic precipitator (ESP) uses a high-voltage electric field to capture dust (efficiency ≥99%), and then generates CaF₂ (reaction efficiency ≥95%) by spraying calcium powder (CaO) and HF, and finally the product is captured by a bag dust collector.
Advantages: Suitable for large flue gas volume (>100,000 m³/h) scenarios, low calcium powder cost (about 500 yuan/ton), but attention should be paid to the compliance disposal of CaF₂ solid waste.
(2) Wet purification technology
Scrubber + Demisting + Neutralization treatment
Process:
Flue gas passes through the scrubber (spraying NaOH solution, pH=10-12) to absorb HF and react to generate NaF;
Demister (wire mesh or cyclone plate) removes water vapor, droplet content <50mg/m³;
After the wastewater passes through the neutralization tank (adding H₂SO₄ to adjust the pH to 6-9), Mg (OH)₂ and other sediments are removed through the sedimentation tank.
Efficiency: Fluoride removal rate ≥98%, dust ≤5mg/m³, but a wastewater treatment system is required, and there is a problem of flue gas "white plume" (water vapor condensation).
(3) Integrated composite process
“Waste heat recovery + dry dust removal + wet defluorination” combination
Application scenario: high-end magnesium casting production line (such as aerospace parts), requiring ultra-low pollutant emissions (dust ≤ 5mg/m³, fluoride ≤ 0.5mg/m³).
Technical points:
The waste heat boiler recovers flue gas heat for preheating combustion air, with an energy saving rate of 15%-20%;
The dry section uses a pulse bag dust collector (filter bag accuracy 0.2μm);
The wet section uses a two-stage scrubber (NaOH+Na2S solution) to ensure deep removal of fluorides.
三. Environmental protection technology innovation and trends
1. Development of new environmentally friendly fluxes
Develop fluorine-free fluxes (such as MgO-CaO-Al₂O₃ system) to reduce fluoride emissions from the source. A composite oxide flux developed by a Japanese company reduces the flue gas fluoride concentration to below 1mg/m³, and the slag can be directly used as paving materials.
2. Intelligent flue gas monitoring system
Deploy online monitoring instruments (such as laser dust monitors and infrared fluoride analyzers) to adjust the parameters of dust removal and desulfurization equipment in real time. A magnesium alloy die-casting plant uses a PLC control system to control the fluctuation of flue gas treatment energy consumption within ±5%, saving 100,000 kWh of electricity per year.
3. Carbon footprint management and carbon neutrality
Some companies offset the carbon emissions in the smelting process by purchasing green electricity and installing photovoltaic power stations. For example, the magnesium casting workshop of Tesla's Shanghai factory uses 100% renewable electricity, and the carbon emissions of the flue gas treatment system are 80% lower than those of traditional processes.
Summary: From "end-of-pipe treatment" to "green manufacturing"
The environmental protection of magnesium casting production needs to be driven by "technological innovation + management optimization": smelting flue gas treatment needs to select dry/wet/composite processes according to production capacity and emission requirements, and clean production (such as fluorine-free smelting and waste recycling) should be implemented throughout the process. As environmental protection standards become stricter (such as the special emission limits for the magnesium industry that China plans to implement in 2025), low-pollution, low-energy magnesium casting production technology will become the core competitiveness for industry access.
Email：cast@ebcastings.com
In the production of magnesium castings, the realization of environmental protection requirements needs to run through the entire process of smelting, casting, and post-processing, and smelting flue gas treatment is a key link. The following is an explanation from two aspects: environmental protection measures system and flue gas treatment technology:
一. Environmental protection measures for the entire process of magnesium casting production
1. Smelting link: source pollution control and energy optimization
Low-pollution smelting technology
Use inert gas protection smelting (such as CO₂, SF₆ mixed gas) to replace traditional fluoride salt flux and reduce the emission of toxic gases such as hydrogen fluoride (HF) and chlorine (Cl₂). For example, a German factory uses CO₂+0.1% SF₆ protection, and the fluoride concentration in the flue gas is reduced from 50mg/m³ to below 5mg/m³ (EU emission standard is 10mg/m³).
Promote the use of electric induction melting furnaces to replace oil furnaces, increase the power conversion rate to 85% (oil furnaces are about 60%), and reduce NOx emissions by 40%-60%.
Waste recovery and energy consumption control
Establish a closed circulation system to process magnesium chips, gate materials and other waste materials through crushing-screening-remelting, with a recovery rate of more than 95%. A domestic enterprise reduces solid waste emissions by 2,000 tons and energy consumption by 12% each year through direct waste remelting technology.
2. Casting and post-processing: process innovation to reduce pollution
Less/no cutting process
High-pressure die casting achieves near-net forming of magnesium castings (dimensional tolerance ±0.1mm), reduces machining processes, reduces cutting fluid usage by 70%, and reduces waste generation by 50%.
Green surface treatment
Use chromium-free passivation (such as silane treatment, rare earth conversion film) instead of hexavalent chromium electroplating, and wastewater COD (chemical oxygen demand) is reduced from 500mg/L to below 100mg/L. For example, a new energy vehicle battery shell uses silane coating, which has a salt spray test of 1,000 hours without corrosion, and reduces wastewater treatment costs by 30%.
3. Comprehensive waste management
Wastewater treatment
Establish a three-level treatment system: regulating tank (neutralizing pH value) → chemical precipitation (removing heavy metal ions) → membrane filtration (COD removal rate 90%), the effluent can be reused in the cooling system, and the water reuse rate reaches 85%.
Classification and disposal of solid waste
After the smelting slag is magnetically separated to recover magnesium metal, the remaining slag is used to produce refractory materials; the waste release agent is regenerated by distillation, and the recovery rate reaches 80%.
二. Core technology for magnesium smelting flue gas treatment
1. Flue gas composition and characteristics
Main pollutants: MgO dust (accounting for 60%-70%), fluoride (HF, MgF₂), trace metal vapor (such as Zn, Pb) and organic volatiles (decomposition products of release agent).
Flue gas characteristics: high temperature (300-500℃), fine dust particle size (0.1-10μm), and highly corrosive fluoride.
2. Mainstream treatment technologies and process combinations
(1) Dry purification technology
Bag dust removal + activated carbon adsorption
Principle: The flue gas is first cooled to 120-150℃ by the waste heat boiler, then passed through a bag dust collector (filter bag material is PTFE, filtration efficiency ≥99.9%) to remove MgO dust, and finally through an activated carbon adsorption tower to remove fluoride and organic pollutants.
Case: A magnesium alloy wheel hub factory adopts this process, and the dust emission concentration is <10mg/m³, and the fluoride is <1mg/m³, which meets the special emission limit values of China's "Industrial Furnace Air Pollutant Emission Standard" (GB 9078-1996).
Electrostatic precipitator + dry defluorination
Principle: The electrostatic precipitator (ESP) uses a high-voltage electric field to capture dust (efficiency ≥99%), and then generates CaF₂ (reaction efficiency ≥95%) by spraying calcium powder (CaO) and HF, and finally the product is captured by a bag dust collector.
Advantages: Suitable for large flue gas volume (>100,000 m³/h) scenarios, low calcium powder cost (about 500 yuan/ton), but attention should be paid to the compliance disposal of CaF₂ solid waste.
(2) Wet purification technology
Scrubber + Demisting + Neutralization treatment
Process:
Flue gas passes through the scrubber (spraying NaOH solution, pH=10-12) to absorb HF and react to generate NaF;
Demister (wire mesh or cyclone plate) removes water vapor, droplet content <50mg/m³;
After the wastewater passes through the neutralization tank (adding H₂SO₄ to adjust the pH to 6-9), Mg (OH)₂ and other sediments are removed through the sedimentation tank.
Efficiency: Fluoride removal rate ≥98%, dust ≤5mg/m³, but a wastewater treatment system is required, and there is a problem of flue gas "white plume" (water vapor condensation).
(3) Integrated composite process
“Waste heat recovery + dry dust removal + wet defluorination” combination
Application scenario: high-end magnesium casting production line (such as aerospace parts), requiring ultra-low pollutant emissions (dust ≤ 5mg/m³, fluoride ≤ 0.5mg/m³).
Technical points:
The waste heat boiler recovers flue gas heat for preheating combustion air, with an energy saving rate of 15%-20%;
The dry section uses a pulse bag dust collector (filter bag accuracy 0.2μm);
The wet section uses a two-stage scrubber (NaOH+Na2S solution) to ensure deep removal of fluorides.
三. Environmental protection technology innovation and trends
1. Development of new environmentally friendly fluxes
Develop fluorine-free fluxes (such as MgO-CaO-Al₂O₃ system) to reduce fluoride emissions from the source. A composite oxide flux developed by a Japanese company reduces the flue gas fluoride concentration to below 1mg/m³, and the slag can be directly used as paving materials.
2. Intelligent flue gas monitoring system
Deploy online monitoring instruments (such as laser dust monitors and infrared fluoride analyzers) to adjust the parameters of dust removal and desulfurization equipment in real time. A magnesium alloy die-casting plant uses a PLC control system to control the fluctuation of flue gas treatment energy consumption within ±5%, saving 100,000 kWh of electricity per year.
3. Carbon footprint management and carbon neutrality
Some companies offset the carbon emissions in the smelting process by purchasing green electricity and installing photovoltaic power stations. For example, the magnesium casting workshop of Tesla's Shanghai factory uses 100% renewable electricity, and the carbon emissions of the flue gas treatment system are 80% lower than those of traditional processes.
Summary: From "end-of-pipe treatment" to "green manufacturing"
The environmental protection of magnesium casting production needs to be driven by "technological innovation + management optimization": smelting flue gas treatment needs to select dry/wet/composite processes according to production capacity and emission requirements, and clean production (such as fluorine-free smelting and waste recycling) should be implemented throughout the process. As environmental protection standards become stricter (such as the special emission limits for the magnesium industry that China plans to implement in 2025), low-pollution, low-energy magnesium casting production technology will become the core competitiveness for industry access.
Email：cast@ebcastings.com
