The production of galvanized fireproof iron sheets requires a balance between improved fire resistance and environmental pollution control. Process optimization must focus on two core areas: the galvanizing process and fireproofing. This can be achieved through measures such as replacing materials with environmentally friendly alternatives, precise control of process parameters, resource utilization of waste, and the application of clean energy, leading to a green transformation of the entire process.
Environmental pollution from the galvanizing process mainly stems from the emission of zinc vapor, acid mist, and zinc-containing wastewater. In traditional hot-dip galvanizing processes, the zinc bath temperature needs to be controlled at around 450℃. During this process, zinc vapor easily volatilizes, forming particulate pollution. Optimization directions include: adopting zinc pot sealing technology to reduce zinc vapor escape through a fully enclosed zinc pot design; and adding a zinc vapor condensation and recovery device to cool the volatilized zinc vapor into zinc powder for reuse in the galvanizing bath, reducing both zinc consumption and air pollution. Hydrochloric acid mist generated during the pickling process is another source of pollution. This can be addressed by installing an acid mist absorption tower, using sodium hydroxide solution spraying to neutralize the hydrochloric acid mist, converting it into sodium chloride solution for reuse in the pickling and rinsing process, achieving an acid mist recovery rate of over 95%.
The environmental impact of fireproofing treatment is concentrated in the emissions of volatile organic compounds (VOCs) from fire-retardant coatings. Traditional fire-retardant coatings contain organic solvents, which easily release harmful substances such as benzene and toluene during application. Optimization solutions include: using water-based fire-retardant coatings, replacing organic solvents with water as a diluent to reduce VOC emissions at the source; and employing chromium-free passivation technology instead of traditional chromate passivation, using silane passivating agents to form a dense oxide film on the zinc plating surface, meeting fireproofing requirements while avoiding heavy metal pollution. Furthermore, the spraying process for fire-retardant coatings can be upgraded to electrostatic spraying or robotic spraying, reducing overspraying and waste through precise control of coating dosage.
Wastewater treatment during the production process is a key aspect of environmental optimization. Zinc plating wastewater mainly contains zinc ions, hydrochloric acid, and trace amounts of heavy metals. It requires a combined process of neutralization precipitation, membrane filtration, and ion exchange: first, calcium hydroxide is added to adjust the pH to alkaline, causing zinc ions to precipitate as zinc hydroxide; then, reverse osmosis membrane separation is used to separate the clear water for reuse in the rinsing process, reducing fresh water consumption; finally, ion exchange resin is used for deep treatment to ensure the zinc content in the effluent is below 2 mg/L, meeting the requirements of the "Integrated Wastewater Discharge Standard." Pickling sludge contains iron oxide and ferrous chloride, which can be decomposed into iron oxide red (used in coatings and building materials) and hydrochloric acid (recycled in the pickling process) through high-temperature calcination, achieving a resource utilization rate of over 80%.
Solid waste treatment must adhere to the principles of "reduction, resource recovery, and harmlessness." The zinc slag produced by hot-dip galvanizing contains 50%-70% zinc, which can be separated into zinc ingots with a purity ≥98% using a centrifuge and reused in the galvanizing furnace; waste flux (containing ammonium chloride and zinc chloride) can be recovered by evaporation and crystallization to obtain ammonium chloride, which can then be used as agricultural fertilizer or electroplating additives. Furthermore, scrap metal and waste packaging materials generated during production must be collected separately and remelted to reduce the extraction of primary resources.
Energy consumption optimization is a crucial way to reduce carbon emissions. Annealing furnaces, as major energy-consuming equipment, can use natural gas instead of coal as fuel, reducing CO₂ emissions; installing waste heat recovery devices allows the heat from annealing furnace exhaust gases (approximately 500°C) to preheat combustion air, saving 20%-30% of natural gas; and using continuous annealing furnaces instead of batch furnaces reduces energy consumption by 30% through heat recycling. Simultaneously, introducing an intelligent control system monitors parameters such as zinc melt temperature and air knife pressure in real time, avoiding energy waste caused by parameter fluctuations.
The application of clean production technologies can further improve environmental protection levels. For example, lead-free zinc plating processes, by adding rare earth elements to modify the zinc bath, maintain the corrosion resistance of the coating while avoiding lead pollution; low-noise air knife technology is applied, reducing noise emissions during zinc plating thickness control by optimizing the air knife structure; and alkaline mist recovery systems are promoted to collect alkaline mist generated during the degreasing process and reuse it in the preparation of degreasing solutions, reducing the consumption of chemical agents.
Environmental optimization of galvanized fireproof iron sheet needs to be integrated throughout the entire production cycle, from raw material selection to waste treatment, from process design to equipment upgrades, all guided by "green manufacturing." Driven by both technological innovation and management improvement, enterprises can not only meet increasingly stringent environmental regulations but also reduce production costs through resource recycling, achieving a win-win situation for both economic and environmental benefits. In the future, with the advancement of "dual carbon" goals, the galvanized fireproof iron sheet industry will accelerate its transformation towards low-carbon and circular economy, becoming a model of green development in the steel deep processing sector.
