Basic Wastewater Terms: What Is Polyferric Sulfate
Chinese chemical name: Polyferric sulfate, solid polyferric sulfate (abbreviated as solid poly-iron or SPFS)
In addition, many factors must be considered in practical engineering applications.
Hazardous component: ferric sulfate (polymerized)
Building on this, industry experts have also carried out extensive research and improvements.
A new, high-quality, and highly efficient iron-salt inorganic polymer flocculant, mainly used for excellent water purification with good water quality. It contains no harmful substances such as aluminum, chlorine, or heavy-metal ions, and has no water-phase transfer of iron ions. It is non-toxic, harmless, safe, and reliable, with significant effects such as turbidity removal, decolorization, de-oiling, dewatering, sterilization, deodorization, algae removal, and removal of COD, BOD, and heavy-metal ions from water. It is also widely used in industrial wastewater treatment, such as printing and dyeing wastewater, and has broad applications in casting, papermaking, pharmaceuticals, and tanning.
In addition, this technology has also been widely applied and practiced in related fields.
4. Significant effects such as turbidity removal, decolorization, de-oiling, dewatering, sterilization, deodorization, algae removal, and removal of COD, BOD, and heavy-metal ions from water;
5. Adapts to a wide pH range of 4–11, with the optimal pH range being 6–9; after purification, the variation in the raw water's pH and total alkalinity is small;
6. Significant purification effect on slightly polluted, algae-containing, low-temperature, and low-turbidity raw water, and especially good on high-turbidity raw water;
When polyferric sulfate is used to treat rare-earth industry wastewater, for example, the device keeps the fine solid particles in the wastewater and the high-concentration ion-membrane surface at a constant distance, greatly reducing the chance for harmful substances to contact and foul the membrane surface, and improving water circulation. This process not only separates and enriches ammonium chloride from the high-concentration rare-earth extraction wastewater and recovers it after meeting industry standards, but also, through electrolysis and solar-driven hydrochloric-acid/ammonia recovery reactors, reduces raw-material consumption in rare-earth production. Using fuel cells to recover energy from large volumes of wastewater—at a treatment cost of 40 yuan for 1,600 t/d of wastewater containing 100 g/L ammonium chloride—this process can generate a profit of 110,000 yuan from the recovered hydrochloric acid and ammonia water. This not only helps the country achieve the goals of reduction, stabilization, and harmlessness in wastewater treatment and disposal; under the premise of safe, eco-friendly, and economical recovery, it utilizes the energy and resources in wastewater and exhaust gas to realize comprehensive wastewater and exhaust-gas treatment and utilization, energy conservation, emission reduction, and the development of a circular economy.
Polyferric sulfate uses a combination of electrophoretic dielectric technology and osmotic membrane separation technology for wastewater reuse treatment, realizing innovation and technological progress in wastewater treatment, giving full play to the investment and operational efficiency of equipment, suited to China's national conditions and the characteristics of Inner Mongolia's wastewater-treatment new technologies, new polyferric sulfate technologies, and new equipment. If widely applied, this new technology will improve the level of industrial wastewater treatment and disposal for mining enterprises in the region, further protect and improve the ecological environment, and promote the sustainable economic, social, and environmental development of the region.
Flocculation technology is widely used in oily wastewater treatment because of its strong adaptability and ability to remove emulsified and dissolved oils as well as some complex macromolecular organics that are difficult to biodegrade. Commonly used flocculants mainly fall into three categories: inorganic, organic, and composite flocculants.
Among inorganic polymer flocculants, polyaluminum chloride and polyferric sulfate have good treatment effects at lower molecular weights, low price, low dosage, and high efficiency, and are therefore widely used.
1. Printing and dyeing wastewater treatment: replacing traditional low-molecular iron and aluminum salts as coagulants. Compared with traditional coagulants that require large dosages, have low coagulation efficiency, and tend to leave residual aluminum ions causing secondary pollution, the dosage of polyferric sulfate is around 150 ppm—small dosage, high removal rates of COD and color, with an optimal pH condition of 8.0. [2]
2. Electroplating wastewater treatment: can be used as a coagulant and de-complexing agent. The complexes are mainly copper–ammonia complexes, which are stable (pH = 11) and difficult to precipitate directly with alkali, polyaluminum chloride, etc. It can also be used for reclaimed-water reuse.
3. Papermaking wastewater treatment: replacing polyaluminum chloride, aluminum sulfate, etc. as a coagulant, and also usable for papermaking sludge dewatering. In the white-water recovery process of papermaking wastewater treatment, polyferric sulfate (a polymer containing strong cations) must not be used—only polyaluminum chloride may be used.
The preparation of polyferric sulfate mainly uses the direct oxidation method and the catalytic oxidation method. Most PFS preparation uses the direct oxidation method, which has a relatively simple process route, can reduce equipment investment and production steps for industrial production, and lower equipment costs, but this production process must rely on oxidants such as H2O2, KClO3, and HNO3 as inorganic oxidants. The catalytic oxidation method generally selects a catalyst and uses oxygen or air oxidation to prepare polyferric sulfate. The following are the specific operating methods for preparing polyferric sulfate:
2FeSO4 + H2O2+ (1-n/2)H2SO4—→Fe2(OH)n(SO4)3-n/2+ (2-n)H2O
During preparation, according to the production volume and required basicity, add ferrous sulfate, water, and sulfuric acid to the reactor and mix. When the temperature rises to 30–45°C, slowly add H2O2 through the feed pipe at the bottom of the reactor while stirring. H2O2 quickly oxidizes ferrous iron to ferric iron; sampling and analysis are performed, and the reaction is stopped when the ferrous concentration drops to the specified level.
Producing polyferric sulfate by this method features simple equipment, short production cycle, no catalyst needed in the reaction, no impurities in the product, and high stability. However, during the reaction, O2 is released as H2O2 decomposes, and without a catalyst it does not act as an oxidant. To reduce O2 generation, the feeding rate of H2O2 must be controlled; the process is batch-operated, affecting production efficiency. H2O2 is relatively costly, which increases the production cost of polyferric sulfate and is unfavorable for industrial production.
In addition, from the perspective of industrial development, market demand is also driving technological progress.
6FeSO4 + KClO3 + 3(1-n/2)H2SO4 —→ 3[Fe2(OH)n(SO4)3-n/2]+ 3(1-n)H2O + KCl
During preparation, add sulfuric acid, ferrous sulfate, and water to the reactor in proportion, and add potassium chlorate while stirring at room temperature or slightly elevated temperature. The process ends when the ferrous ion concentration drops to the specified level.
This method has a simple production process, low equipment investment, good product stability, and high reaction efficiency, with no air pollution. The product contains chlorate and can serve both as coagulant and bactericide. However, it retains relatively high chloride and chlorate ions, making it unsuitable for drinking-water treatment. Also, because potassium chlorate is expensive, the product cost is high.
In addition, from the perspective of industrial development, market demand is also driving technological progress.
The produced chlorine gas still acts as an oxidant, oxidizing ferrous iron to ferric iron. However, a small amount of chlorine escapes as gas and is wasted, so it cannot be fully utilized. At the same time, it causes environmental pollution and adds post-treatment steps. Sodium hypochlorite is an alkaline oxidant; when preparing polyferric sulfate with it, the dosage of H2SO4 is high to lower the pH. The product prepared by this method has poor stability and is not suitable for long-term storage.
In addition, many factors must be considered in practical engineering applications.
The NO2 generated by the reaction can also act as an oxidant, so the oxidation efficiency of HNO3 is high.
This method uses industrial ferrous sulfate as raw material, oxidizes it with industrial sulfuric acid and then with industrial concentrated nitric acid. FeSO4:HNO3 is 1:(0.20–0.30):(0.10–0.32); the added water is less than 20% of the total of the three; air or oxygen is blown in abundantly while stirring at 0.1–0.2 MPa, oxidized at 50–70°C, and hydrolyzed and polymerized at 102–103°C. The reaction cycle is controlled within 30–60 min.
When HNO3 is used for oxidation, the cost is relatively low and the reaction cycle is short. The resulting product has high concentration and is easy to make into a solid product. If industrial first-grade raw materials are selected, the product can be used for drinking-water treatment. However, the NO2 generated in the reaction causes environmental pollution and requires a dedicated absorption device for treatment.
In summary, although the direct oxidation method has a simple process and is easy to operate, it suffers from problems such as large oxidant dosage, high cost, the need to separate out ions introduced by the oxidant, and the need for dedicated equipment to absorb and treat harmful gases generated in the reaction, making it difficult to popularize and apply in industrial production. However, when a small amount of polyferric sulfate is needed for experimental research, this method is simple and feasible to prepare.
That is, using ferrous sulfate and sulfuric acid as raw materials, with the help of a catalyst (NaNO2), an oxidant is used to oxidize ferrous sulfate to ferric ions in an acidic medium. Then sodium hydroxide is used for neutralization to adjust the basicity, and hydrolysis and polymerization reactions produce polyferric sulfate.
Polyferric aluminum sulfate liquid: add dilute sulfuric acid at about 3% concentration to ferrous sulfate, then add sodium nitrite at a ratio of about 3:100 to ferrous sulfate, blow in air or oxygen for oxidation, and prepare polyferric sulfate through hydrolysis and polymerization reactions.
1. Using liquid ferrous iron as raw material, using air as the oxidant, it goes through low-temperature dehydration, crushing, high-temperature oxidation, cooling, poly-condensation, solidification, aging, crushing to finished product.
(1) Toxic hazards of aluminum: aluminum is a slowly acting toxicant that accumulates in tissues such as brain cells after entering the human body through water, and long-term drinking of tap water treated with aluminum coagulants can cause dementia, cardiovascular disease, osteoporosis, kidney dysfunction, and other stubborn diseases. According to data from the China Committee of the International Alzheimer's Association, there are more than 24 million Alzheimer's patients worldwide, of which more than 7 million are in China, increasing at a rate of 300,000 new patients per year. The permissible aluminum content in drinking-water quality standards of Western developed countries is 0.05 mg/L. The aluminum content in China's tap water exceeds this value by several times.
(2) Corrosion of water-supply pipelines: because the electrochemical corrosion problem of tap-water pipelines has not been solved, the turbidity, color, iron content, bacteria, and other water-quality indicators at the user's tap rise substantially, further worsening tap-water quality. Due to corrosion, corrosive deposits form on the inner walls of supply metal pipes, the flow resistance keeps increasing, and the power consumption for water supply rises year by year, causing huge energy losses. After corrosion perforates the supply pipelines, large amounts of tap water leak away, and the service life of supply pipelines is greatly shortened.
Because raw-water properties vary, according to different situations, on-site commissioning or beaker tests should be performed to obtain the best operating conditions and optimal dosage for the best treatment effect.
1. Before use, put this product into a dissolving tank at a certain concentration (10–30%) and inject tap water, stirring to fully hydrolyze, then let it stand until it becomes
a reddish-brown liquid, then dilute with water to the required concentration for coagulation dosing. Water plants can also prepare a 2–5% solution for direct dosing; industrial wastewater treatment can directly prepare
In addition, many factors must be considered in practical engineering applications.
1/3–1/4. If a liquid product was originally used, it can be calculated based on the corresponding agent concentration. Roughly determined by a weight ratio of 1:3.
In addition, from the perspective of industrial development, market demand is also driving technological progress.
7. This product is applied to environmental protection and industrial wastewater treatment; the usage method is roughly the same as that of a water-treatment plant. For raw water with high color, high COD, and high BOD,
In addition, from the perspective of industrial development, market demand is also driving technological progress.
The method steps are as follows: in an acidic solution, use stannous chloride to reduce ferric iron to ferrous iron. The excess stannous chloride is removed with mercuric chloride, then titrated with a standard potassium dichromate titrant.
In addition, from the perspective of industrial development, market demand is also driving technological progress.
Health hazards: This product irritates the skin and mucous membranes. Inhaling high concentrations can cause bronchitis, and in some individuals, bronchial asthma. Large accidental ingestion can cause oral erosion, gastritis, gastric bleeding, and mucosal necrosis. Chronic effects: long-term contact can cause headaches, dizziness, loss of appetite, cough, nasal congestion, chest pain, and other symptoms.
In addition, many factors must be considered in practical engineering applications.
Inhalation: quickly move the victim to fresh air. Keep the airway clear. If breathing is difficult, give oxygen. If breathing stops, perform artificial respiration immediately. Seek medical attention.
Building on this, industry experts have also carried out extensive research and improvements.
Emergency handling: isolate the contaminated leak area and restrict access. Emergency responders should wear dust masks (full-face) and acid-alkali resistant protective clothing. Do not touch the leak directly.
In addition, from the perspective of industrial development, market demand is also driving technological progress.
Handling precautions: operate in an enclosed manner with local exhaust ventilation. Operators must receive special training and strictly follow operating procedures. Operators should wear self-priming filter dust masks, chemical-safety goggles, rubber acid-alkali resistant clothing, and rubber acid-alkali resistant gloves. Keep away from flammable and combustible materials. Avoid generating dust. Avoid contact with alkalis and alcohols. Pay special attention to avoiding contact with water. Handle with care during loading and unloading to prevent damage to packaging and containers. Equip with leak-emergency handling equipment. Empty containers may retain harmful substances.
Storage precautions: store in a cool, dry, well-ventilated warehouse. Keep away from fire and heat sources. Keep relative humidity below 75%. Packaging must be sealed and must not be allowed to get damp. Store separately from flammable (combustible) materials, alkalis, alcohols, etc.; never store mixed. Do not store for long periods to avoid deterioration. The storage area should be equipped with suitable materials to contain leaks.
It is worth noting that the technologies and standards in this field are also continuously developing and improving.
Respiratory protection: when likely to contact its dust, wear a self-priming filter dust mask; for emergency rescue or evacuation, wear an air respirator.
In addition, from the perspective of industrial development, market demand is also driving technological progress.
Other protection: smoking, eating, and drinking are prohibited at the work site. After work, take a shower and change clothes. Store clothes contaminated with poison separately and wash before reuse. Maintain good hygiene habits.
In addition, many factors must be considered in practical engineering applications.
Rail transport must strictly follow the dangerous-goods loading table in the Ministry of Railways' 'Rules for the Transport of Dangerous Goods.' At departure, packaging must be intact and loading stable. During transport, ensure containers do not leak, collapse, fall, or be damaged. Strictly prohibit mixed loading and transport with flammable or combustible materials, alkalis, alcohols, food chemicals, etc. Transport vehicles should be equipped with leak-emergency handling equipment. During transport, protect from sun exposure, rain, and high temperatures.
Regulations such as the 'Chemical Dangerous Goods Safety Management Regulations' (promulgated by the State Council on February 17, 1987), the 'Implementation Details for the Chemical Dangerous Goods Safety Management Regulations' (Hua Lao Fa [1992] No. 677), and the 'Regulations on the Safe Use of Chemicals in the Workplace' ([1996] Lao Bu Fa No. 423) all stipulate corresponding provisions for the safe use, production, storage, transport, and loading/unloading of chemical dangerous goods.
This product is widely used in the purification treatment of domestic drinking water, industrial circulating water, and wastewater from industries such as chemicals, petroleum, mining, papermaking, printing and dyeing, brewing, steel, and gas, achieving ideal results for different water sources in different regions.
When using, generally prepare liquid polyferric sulfate into a 10%–50% aqueous solution (it can be dosed directly when the raw-water turbidity is high); prepare solid polyferric sulfate into a 10%–30% aqueous solution, then add the prepared solution at the optimal conditions and dosage according to specific circumstances, and obtain the best coagulation effect after full stirring.
The dosage can be determined according to the different turbidity of the raw water. For generally turbid water (turbidity 100–500 mg/L), use 30–50 kg of this product per 1,000 tons; for non-drinking high-turbidity industrial sewage, the dosage can be appropriately increased.
For industrial wastewater treatment, dilute first-grade polyferric sulfate to a 1–2 times aqueous solution. When the raw-water concentration is high and the treated water volume is large, it can be dosed directly. Then, according to the results of laboratory simulation tests, add at the optimal process conditions and dosage; after full stirring, coagulation, and settling, clear effluent can be obtained.
Water-purification plants can also dilute 2–5 times before dosing. The dosing amount is determined according to the raw-water properties through production commissioning or beaker experiments based on the formation of flocs; water plants can use the dosage of other agents originally used as a reference. Under the same conditions, the dosage of this product is roughly equivalent to that of solid polyaluminum chloride, and is 1/2–1/3 of that of solid aluminum sulfate. If a liquid product was originally used, it can be calculated based on the corresponding agent concentration, roughly by a weight ratio of 1:3.
A large amount of practice has proven that ordinary polyferric sulfate is difficult to achieve the expected purpose in most cases. Generally, it is necessary to select the agent type and preliminary dosage through dosing experiments based on the medium and location of use, and then conduct industrial dynamic experiments to determine the optimal dosing point and dosage. This will help continuously expand the application scope of polyferric sulfate in the mining and metallurgy fields.
