2026/06/29
Phosphogypsum is an industrial solid waste generated during the wet-process phosphoric acid production. For every ton of phosphoric acid produced, 4-5 tons of phosphogypsum are produced as a byproduct. my country's annual increase in phosphogypsum production is approximately 77 million tons, with historical stockpiles exceeding 820 million tons, and a comprehensive utilization rate of only about 50%. The soluble phosphorus, fluorine, and heavy metals it contains not only restrict resource utilization but also easily lead to environmental risks such as groundwater pollution. Achieving phosphogypsum volume reduction requires a coordinated approach across three stages: washing processes, neutralization, and resource utilization.
I. Washing Process: From "Water-Consuming Giant" to "Water Efficiency Revolution"
Washing is the first step in removing soluble impurities from phosphogypsum. Soluble P₂O₅ and F⁻ in phosphogypsum are easily soluble in water, and washing can remove most of these impurities. Traditional washing processes suffer from high water consumption and low impurity removal rates.
Multi-stage countercurrent washing is currently the most advanced solution. This technology utilizes the high-concentration wastewater after washing as the initial washing liquid, achieving a tiered recycling of water resources. The liquid-to-solid ratio is reduced to 1:1, resulting in a water saving rate of 66%. Combined with phosphogypsum crystal modification technology, the removal rates of soluble phosphorus and fluoride are increased to over 95% and 90%, respectively, with the water-soluble phosphorus pentoxide content in the product consistently below 0.1%.
Core equipment includes multi-stage series washing tanks (equipped with agitators and pumping systems), belt filters or vertical filters, hydrocyclones, and vacuum dewatering systems. Some advanced units have achieved integrated continuous equipment for "flotation—multi-stage countercurrent washing—modification," increasing the single-line processing capacity to 138 tons/hour of dry-based phosphogypsum.
II. Neutralization Treatment: From Acidic Waste to Neutral Resource
The washed phosphogypsum remains acidic and requires neutralization treatment to adjust the pH value and solidify residual harmful substances.
Lime neutralization is the most widely used process—by adding alkaline substances such as quicklime or hydrated lime, residual acid in phosphogypsum is neutralized, while soluble phosphorus and fluorine are converted into inert, insoluble salts. This method is simple, requires low investment, does not produce secondary pollution, and the treated phosphogypsum meets the requirements for use in building materials. Studies have shown that lime neutralization is effective in removing soluble phosphorus and is more economical and applicable than other pretreatment methods.
Neutralization equipment mainly includes a slurry mixing tank, a lime slurry preparation and dosing system, a neutralization reaction tank, and a solid-liquid separation device. For large-scale treatment, a precise neutralizing agent metering and pH online monitoring system is required to ensure stable treatment results.
III. Resource Utilization Machinery: From Solid Waste to Building Materials
After washing and neutralization, phosphogypsum is ready for resource utilization and can be transformed into high-value-added products through specialized equipment.
The building materials sector is the largest application area. After drying, calcining, and grinding, phosphogypsum can be used to prepare building gypsum powder, gypsum blocks, gypsum boards, etc. Core equipment includes: an externally heated rotary kiln, a double-pass direct-heated calcining kiln, and a vertical grinding mill or ultrafine ring roller mill. Producing sulfuric acid and cement from phosphogypsum is an important way to achieve large-scale waste disposal—more than 2 tons of phosphogypsum are consumed for every ton of sulfuric acid and ton of cement clinker produced.
In summary, the reduction of phosphogypsum volume involves a complete technological chain of "washing and impurity removal—neutralization and solidification—resource transformation." Multi-stage countercurrent washing achieves source reduction, lime neutralization completes harmless modification, and building materials and chemical equipment transform waste into high-value products. Only through the synergy of these three aspects can phosphogypsum be transformed from an "ecological burden" into a "resource asset."
The three‑step approach—multi‑stage countercurrent washing, lime neutralization, and resource conversion—transforms phosphogypsum from a hazardous industrial waste into a valuable secondary raw material. This volume‑reduction chain is not only an environmental imperative but also a strategic link to the broader fertilizer industry. Purified phosphogypsum can serve as a calcium‑sulfur source in npk fertilizer raw materials processing, complementing traditional phosphate rock and potash inputs. When integrated into npk fertilizer formula processing, the refined gypsum contributes to balanced nutrient formulations, particularly for sulfur‑demanding crops, while reducing reliance on virgin mineral extraction. Advanced inorganic fertilizer machine systems, including dryers, crushers, and mixers, can be adapted to handle the neutralized phosphogypsum, blending it with urea, MAP, and KCl to produce customized NPK grades. The npk fertilizer manufacturing process benefits from the consistent quality of washed and neutralized gypsum, which improves granulation efficiency and product hardness. Furthermore, a fertilizer drying and cooling machine ensures that the final compound fertilizer meets strict moisture and strength specifications, preventing caking during storage. By closing the loop between phosphoric acid production and fertilizer manufacturing, this integrated approach not only solves a pressing waste problem but also creates a cost‑effective, sustainable source of secondary nutrients—turning an ecological burden into a competitive advantage for the circular economy.