sulfur once approached the threshold of 10000 yuan per ton, and the price of sulfuric acid rose accordingly.
According to relevant data, in July 2026, the monthly average price of domestic solid sulfur was 9076.35 yuan/ton, and the transaction price of solid sulfur in Lijin, Shandong was once 10,000 yuan/ton; in August, the average price of sulfuric acid in East China rose to 2397.50 yuan/ton, while the annual average price in 2025 was only 605 yuan/ton. According to the industry general unit consumption of about 0.33 tons of sulfur per ton of sulfuric acid, the raw material cost of sulfur-based sulfuric acid production is close to 3000 yuan/ton, which is higher than average price of sulfuric acid in East China, while the sulfur resource of phosphogypsum route comes from waste residue, and the raw material cost is almost zero, which is the real attraction of this route.
This price signal is pushing the project of phosphogypsum acid co-production of cement clinker to a centralized upsurge. According to the announcement of the capacity replacement plan of Hubei Economic and Credit Department, four related projects with a total clinker production capacity of 2.35 million tons were disclosed on July 14 alone, and the 2500 tons/day project of Hubei Sanning Chemical Industry was followed up on August 25, all of which were planned to start within the year. The
policy side is also opening at the same time: Article 12 of the current "Measures for the Implementation of Capacity Replacement in the Cement and Glass Industry (2024 Edition)" (Ministry of Industry and Information Technology [2024] No.206) clearly States that new cement kilns in Hubei, Yunnan, Guizhou, Sichuan and Anhui provinces dispose of phosphorus (titanium, fluorine) gypsum and replace more than 70% of limestone raw materials. The equivalent replacement can be implemented under the condition that the total clinker production capacity in the province does not increase (based on 2020). In the carbon quota allocation plan of the cement industry from 2025, the "production line of Portland cement clinker as a by-product of gypsum sulfuric acid production" is listed as a special case, and its annual quota is equal to the actual carbon emissions after verification.
Capital and capacity indicators are tilting towards this route, but one question is drowned out by the heat of price-who will guard the quality of clinker as a by-product? The soundness of
cement clinker may be affected
. The logic of this process, which is called "double circulation of sulfur and calcium", is not complicated: calcium sulfate in phosphogypsum is disassembled in a reducing atmosphere, sulfur is converted into sulfur dioxide to produce sulfuric acid, and calcium and silicon-aluminum-iron are sintered into cement clinker. The first goal of the enterprise is the sulfur dioxide concentration of kiln gas and the recovery rate of sulfur resources. The technical literature published by the industry shows that the sulfur dioxide concentration at the kiln inlet of such units can only reach about 7%, while the best requirement for entering the sulfuric acid conversion system is more than 10%-once the decomposition is incomplete, the residual calcium sulfate and the intermediate product calcium sulfide will all remain in the clinker.
In the early years, a chemical enterprise in Shandong left very convincing measured data: the control requirement of free calcium oxide in clinker was less than 1.5%, but it once reached 1.89% in actual production; the requirement of sulfur trioxide was less than 1.5%, and it actually reached 2.42%. Free calcium oxide and sulfur trioxide are the most direct indicators to determine the soundness of cement.
This is the structural risk of the process itself. The calcium oxide in the traditional kiln comes from the decomposition of calcium carbonate, and the reaction is "smooth"; the calcium oxide in the co-production kiln comes from the carbon reduction and decomposition of calcium sulfate, and the decomposition temperature is higher and the heat absorption is greater. The carbon here is not only a fuel but also a reducing agent-the carbon is insufficient, and the gypsum is not completely decomposed; the carbon is excessive, and the reducing atmosphere in the kiln is strong, and the ferric iron is reduced to ferrous iron, and the clinker is green, and the strength in the later period is reduced. It is extremely difficult to precisely align the production rate of calcium oxide with the combination and consumption rate of tricalcium silicate and dicalcium silicate, and the extra part is free calcium oxide: after hydration, the volume expands by nearly one time, which is very easy to cause poor stability.
The difficulty is far more than stability, and the whole quality control system needs to be improved
. Stability is only the one that is most easily detected. Because the mineral system of clinker is forced to turn to high dicalcium silicate, the formation of tricalcium silicate is inhibited, the early strength is congenitally inferior, and it is almost inevitable that the three-day strength is lower than that of traditional clinker. The ingredient logic is also completely different: according to the data recorded in the case base of phosphogypsum pollution prevention technology of the Ministry of Ecology and Environment, the lime saturation coefficient of the early production line is only 0.82-0.87, the silicon rate is as high as 3.20-4.20, and the iron rate (also known as aluminum rate) is controlled at 2.00-3.00; There are also technical routes to do the opposite, deliberately making the saturation ratio 1.0 ± 0.02, and using the method of increasing the lime content to offset the risk of free calcium caused by incomplete decomposition. The two sets of values are almost opposite, which shows that the conventional batching experience can not be copied in this process. The source of
fluctuation is not only in the kiln. According to a study (China Gezhouba Group Cement Co., Ltd. Team) published in Cement Engineering, Issue 2, 2026, a systematic test was conducted on the co-production clinker of three representative enterprises. The conclusion is that one enterprise has the worst quality due to low saturation ratio and insufficient grinding; one enterprise has the best comprehensive mechanical properties, but the strength stability is insufficient due to the influence of high phosphorus and fluorine and the fluctuation of kiln conditions; Only one is stable. The congenital mismatch of
raw materials is more alarming-according to the case base of phosphogypsum pollution prevention and control technology of the Ministry of Ecology and Environment, the content of phosphorus pentoxide in phosphogypsum of many enterprises is about 1.5%, while the requirement of the process is not higher than 1.2%. Once the content of phosphorus pentoxide in the raw meal exceeds 1.5%, the eutectic solution will be generated in the firing process, the liquid phase will increase significantly, the firing temperature will be lowered, the load of the device will be reduced, and the quality of the clinker will become poor or even unqualified. Phosphorus will also dissolve into dicalcium silicate, which will induce the transformation of crystal form, the pulverization of clinker and the cliff-like decline of strength. Fluorine is also a double-edged sword: when it is appropriate, it plays a role in mineralization, but once the fluorine content of raw materials increases, the strength of clinker will be significantly reduced, and even rapid setting will occur. In addition, the ring and crust caused by sulfur cycle will further deteriorate the uniformity of clinker quality, and the mineral composition of belite will make the grindability worse, and the strength will not come up and the power consumption will be high if the grinding is insufficient. From
this series of problems, the conclusion is very clear: phosphogypsum acid co-production clinker is not a matter of changing the ingredients of a cement line, but to rebuild a set of quality control system. The faster the
scale, the more the quality account depends on the data to return
the current threshold, which is not ambiguous. GB/T 21372 — 2024 "Portland Cement Clinker" has been implemented on October 1, 2024, with new assessment indicators such as chloride ion content not exceeding 0.06% and radioactivity, and the strength grade of general cement clinker is subdivided into 42.5 and 52.5. It is required that after being made into I type Portland cement, the initial setting shall not be earlier than 45 minutes, the final setting shall not be later than 390 minutes, the stability of boiling method shall be qualified, and the specific surface area of the test mill shall be controlled at 350 ± 10 square meters per kilogram.
For projects that are being demonstrated or have been put into production, there are five things that are recommended to be put forward immediately.
First, the acceptance does not depend on the single qualification, but on the range and standard deviation of the indicators for three to six consecutive months. Free calcium oxide, clinker sulfur trioxide, calcium sulfide, loss on ignition, alkali content, chloride ion, radioactivity and strength of three days and 28 days can not be less.
Secondly, the grinding station is regarded as the most effective referee-the quality disputes of commodity clinker are based on the test results of quality inspection agencies at or above the provincial level, and the downstream re-inspection is harder than self-inspection of the production line.
Third, look at the name and flow direction of the product: whether it is called "clinker" or "cementitious material" or "admixture", whether it is into the mixing station or into the mine filling, the name and direction itself is the self-description of the quality positioning.
Fourthly, attention should be paid to the impurity content in phosphogypsum and how to remove impurities such as phosphorus and fluorine in phosphogypsum at the front end to avoid the impact on kiln calcination and clinker quality.
Fifthly, the indicators of capacity replacement should not only assess the consumption, but also take the continuous quality data and the results of third-party re-inspection as the preconditions for the acceptance of production and the landing of indicators. The
sulphur market will ebb and the sulphuric acid profiteering will subside, but every gram of free calcium oxide left in the concrete will not disappear by itself. If the quality problem can not be effectively controlled, it will ultimately be repaid by the life of the building.
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