Progress on Manufacturing Method of Inorganic
Polymer Coagulant Polyferric salt category
Li Mingyu
( Department of Environmental Engineering, Jinan University, Guangzhou 510632, China. E-mail: liming-yu@sohu.com)
Abstract: This paper gives a review of the manufacturing method of inorganic high polymer coagulant polymerized ferric sulfate. The present situation of the studies and the production of PFS is discussed. It points out the merit and the shortcoming of the manufacturing methods of PFS with ferrous sulfate, pyrite cinder and other slags containing iron. Some suggestions about present problems and development direction in the production of PFS have been put forward.
Key words Polyferric sulfate, ferrous sulfate, coagulant, pyrite cinder
Introduction
Polymerized ferric sulfate(PFS) is a new inorganic high polymer coagulant. Its molecular formula is Fe2(OH)n(SO4)3-n/2]m, (n>2, m=f(n) ). It can be used in waste water treatment and the purification of drinking water[1]. Compared with general inorganic coagulants, for example, ferrous sulfate, ferric chloride, aluminum chloride, aluminum sulfate, alum floc and polymerized aluminum chloride(PAC) , PFS is the best coagulant. Its coagulating ability is strong, sinking speed is quick, and producing cost is low. In addition, the leaving of aluminum is more in the water treated with the coagulants containing aluminum, and it is harmful to the health of human body[2]. This restricts the development of aluminum coagulants, and particularly in drinking water treatment. Nevertheless, the leaving of ferric is little in the water treated with PFS, and it is not harmful to human body. At the same time, PFS is also superior to organic coagulants such as polyacrylamide(PAM) in some industrial wastewater treatment[3]. When PFS substituted for PAM in water treatment, the harm of monomer AM, which was left in water after PAM was degraded, could be avoided. So the application prospect of PFS is very good and the market competition power is stronger in industrial wastewater treatment, industrail using water, and life drinking water.
In 1972, Japan put forward PFS as one of coagulants, and applied for the first patent[4] of PFS made from ferrous sulfate. Then industrial scope production and application in water treatment were formed. China started the studies of PFS in 80's early . The manufacture of PFS made from ferrous sulfate was developed successfully by Tianjin Research Academies of Chemical Industry under Ministry of Chemical Industry of China in 1982. The production of PFS was industrialized[5] in 1984. Hereafter , popularizing application step by step in Wuhan iron and steel company, etc. Now, PFS has been universal concerned and applied in China as a new inorganic high polymer coagulant[6].
At present, the major manufacturing method of PFS is the oxidation method of ferrous sulfate. Ferrous sulfate and sulfuric acid are important raw materials in this method. PFS can be made by the oxidation of ferrous sulfate and the hydrolysis and the polymerization of ferric sulfate. Another method is that some iron ore dregs (or waste residue) and sulfuric acid are used as the raw materials of PFS. Iron ore dregs are dissolved in sulfuric acid, then hydrolysis, polymerization.
1 Manufacture of PFS with ferrous sulfate
In general, ferrous sulfate, which is a by-product produced in the production process of titanium white(titanium dioxide), and sulfuric acid are used as the raw materials of PFS. Besides, acid washing waste liquids, scrap-iron, and sulfuric acid can also be used. In the manufacturing process of PFS, the reactions of oxidation, hydrolysis, and polymerization are all existential at the same time. Because of the cause of dynamics, the oxidizing reaction of ferrous sulfate is slower under acidity condition. So the rate controlling step of the reaction system is the oxidizing reaction. This reaction may be directed oxidation or catalyzed oxidation according to different oxidizing process.
1.1 Method of directed oxidation
The method of directed oxidation is that ferrous sulfate was oxidized directly into ferric sulfate by oxidizer. The oxidizer used here was hydrogen peroxide[7], manganese dioxide, potassium chlorate[8], sodium persulfate, sodium hypochlorite or nitric acid and so on. The oxidizing reaction can be completed within two hours under the condition of room temperature when hydrogen peroxide is used as oxidizer:
2FeSO4 + H2O2 + H2SO4 = Fe2(SO4)3 + 2H2O （1）
Then, hydrolysis and polymerization:
Fe2(SO4)3 + nH2O = Fe2(OH)n(SO4)3-n/2 + n/2H2SO4 （2）
m[Fe2(OH)n(SO4)3-n/2] = [Fe2(OH)n(SO4)3-n/2]m （3）
The time of the oxidizing reaction may be shortened further under the condition of 50℃.
The method of directed oxidation has some merits, such as simple process, easy operation,
and shorter reaction time, but the consumption of oxidizers is high and the price is expensive. So PFS made by the method does not have market competition power.
In the method of directed oxidation, literatures [9] put forward another way which was easy to operate and popularize. The way was based on some features of the instability of ferrous hydroxide and being easy to be oxidize into ferric hydroxide. Firstly, ferrous sulfate was changed into ferrous hydroxide by adding alkali in the solution of ferrous sulfate:
FeSO4 ＋ 2NH3·H2O ＝ Fe(OH)2 ＋ (NH4)2SO4 (4)
Secondly, ferrous hydroxide forming in the reaction above was oxidized into ferric hydroxide after being placed in air:
4Fe(OH)2 ＋ O2 ＋ 2H2O ＝ 4Fe(OH)3 (5)
Then , oxidizer solution was obtained though the reaction between hydrogen peroxide and ferrous sulfate according to the equation ( 1 ). Finally, PFS was made by mixing the ferric hydroxide suspension and the oxidizer solution within 2 hours under the stirred condition.
2Fe(OH)3 ＋ H2SO4 ＋ Fe2(SO4)3 ® [Fe2(OH)n(SO4)3-n/2]m ＋ H2O (6)
These reactions mentioned above can take place in room temperature. The processing equipment of the method are simple and it is easy to operate and the cost of PFS is low too.
Literature [9] reported that the stability of PFS made in this way was poorer. In fact, the instability of PFS made in other methods mentioned in following is existent too. The critical factors affecting the stability are pH, Fe3+/SO42- or adding stabilizer in PFS.
1.2 Method of catalyzing oxidation
The method of catalyzing oxidation is that ferrous sulfate is oxidized into ferric sulfate by oxidizer under the effect of catalyst. It is a major method of manufacturing PFS with ferrous sulfate. Many studies[10-15] have been made in this aspect. Under the conditions of having oxidative catalyst and suitable temperature, PFS can be made through the oxidation of ferrous sulfate, hydrolysis, and polymerization. The catalysts used in the reaction of catalyzing oxidation were sodium nitrite, manganese dioxide or chloride. At present, the most production companies of PFS use this method.
The manufacture of PFS with ferrous sulfate and sulfuric acid was reported firstly by Japan patent[4]. When sodium nitrite and air were used as catalyst and oxidizer respectively, the mechanism of catalyzing oxidation can be showed as follows:
2FeSO4 + H2SO4 + 2NaNO2 ＝ 2Fe(OH)SO4 + Na2SO4 + 2NO (7)
FeSO4 + NO ＝ Fe(NO)SO4 (8)
2Fe(NO)SO4 + 1/2 O2 + H2SO4 ＝ Fe2(SO4)3 + 2NO + H2O (9)
2NO + O2 ＝ 2NO2 (10)
2NO + 1/2 O2 ＝ N2O3 (11)
2FeSO4 + N2O3 + H2O ＝ 2Fe(OH)SO4 + 2NO (12)
or 2FeSO4 + N2O3 + H2SO4 ＝ Fe2(SO4)3 +2NO + H2O (13)
2FeSO4 + NO2 + H2O ＝ 2Fe(OH)SO4 + NO (14)
or 2FeSO4 + NO2 + H2SO4 ＝ Fe2(SO4)3 +NO + H2O (15)
Ferric salts produced in these reactions were hydrolyzed and polymerized:
2mFe(OH)SO4 + (1-n/2)mH2SO4 ＝ [Fe2(OH)n(SO4)3-n/2]m + (2-n)mH2O (16)
or Fe2(SO4)3 + m×nH2O ＝ [Fe2(OH)n(SO4)3-n/2]m + nm/2 H2SO4 (17)
It can be seen from the reactions above that the mechanism of the oxidizing reaction of ferrous sulfate had been changed owing to the participation of NO which made the oxidizing reaction easy. The catalyzing oxidation time was shortened to 4~5 hours from original 17 hours. Even so, the time was still longer and the consumption quantity of catalyst was also more. Meanwhile, nitrogen oxides were discharged into air in the manufacturing process of PFS and this resulted in the environmental pollution.
For the sake of shortening the reaction time, some measures such as heating and high pressure and strong stirring, were often adopted in the manufacturing process. Among them, the method of two steps oxidation could shorten the time. Firstly, ferrous sulfate was oxidized into ferric sulfate under the heating condition. Secondly, both ferrous sulfate and hydrogen peroxide were added in the solution of ferric sulfate made above according to proportion. Then, PFS was obtained after one hour reaction under the stirred condition.
In order to avoid pollution, Shorten further reaction time, and reduce energy consumption, the manufacturing technology and the manufacturing method of PFS had been investigated thoroughly. Some progresses had been made[16], for example, the catalysis oxidizing reaction taken place in a hermetic container and the proportion of SO42-/Fe3+ was controlled in the reaction system. In addition, taking the place of air, oxygen was used as oxidizer. In such situation, PFS was obtaining under the condition of stirring strongly within 1.5~2 hours and 55~90℃ and 29.4-147´104 Pa. Nevertheless these conditions of high temperature and high pressure and strong stirring will increase the difficulty of technology and the investment of equipments.
Further improvement was that the speed of adding sulfuric acid was controlled and sodium nitrite catalyst was added in batches in the oxidizing process of ferrous sulfate. Under the conditions of normal pressure and above 40℃, the oxidizing reaction could achieved within 2-3 hours when oxygen was used as oxidizer[13]. This report thought that the method of adding sulfuric acid, that is the PH of reaction system was controlled in certain scope, was the key of shortening the reaction time. Because the oxidizing reaction of ferrous sulfate was very difficult in the condition of lower PH, but it could take place easily when the PH was higher than 2.
In addition, literature [17] developed a new manufacturing technology of PFS with an atomization method, that is, under the conditions of normal pressure and heating, the atomization drip of ferrous sulfate was contacted with nitrogen dioxide in circulation state. The aim of this process was to raise the contact area between nitrogen dioxide and ferrous sulfate solution, quicken reaction velocity, and shorten production cycle. The process pioneered a new way for the production of PFS. Of course, this will also increase the difficulty of technology and the investment of equipment.
Moreover, it was reported that the best kind of catalyst had been found[18] already up to now. This catalyst was not only high effective but nonpoisonous. When it was used in the oxidizing reaction of ferrous sulfate, the reaction could be completed in two hours. We hope it can be used in the industrial production of PFS early.
In the manufacturing process of PFS above-mentioned, the reaction of ferrous and nitrogen oxides belongs to a reaction between liquid and gas. In order to increase their contact area and quicken the reaction speed, some measures, such as heating, high-pressure, strong stirring, and spraying, were often used. So, the technology of the method is complicated and the investment cost of equipment is also higher.
Besides, in other report, potassium chlorate or hydrogen peroxide were used as a substitute for air or oxygen in the system of sodium nitrite. Although this can quicken the speed of catalysis oxidizing reaction, it increases the product cost, too.
1.3 Effect of catalyst promoter on the reaction of catalyzed oxidation
Because the oxidizing reaction is a rate controlling step in the manufacturing process of PFS, shortening the reaction time has already become a focal point concerned. So people had made thorough studies[3,6,18] at the aspects of oxidizer, catalyst, and catalyst promoter. Literature [3] had made some detailed studies on the kind and the addition of catalysts, the selection of catalyst promoters, the temperature and the acidity of reaction system. This literature thought that sodium iodide as a catalyst promoter could quicken the reaction speed. At the same time, it also thought that controlling the PH of the reaction system was a key to quicken the speed of oxidizing reaction. It discussed how sodium iodide quickens the speed of the oxidizing reaction, too.
On the basis of inspecting the effect of catalysts and oxidizers on the speed of catalysis oxidizing reaction, literature [6] reported that the trace catalyst promoter of HG-1, HG-2, or HG-3 could notably raise the speed in the reaction system of oxygen and sodium nitrite. This made not only the consumption of catalyst decreases one a third but the reaction times shorten two thirds.
In a word, sodium nitrite was generally used as the catalyst in the process of catalysis oxidizing reaction. It shoud be pointed out that sodium nitrite is a carcinogen, and some nitric oxides were let in the process. This results in environmental pollution. In order to simplify technology, cut down the cost of product and decrease pollution, the development direction of PFS made with the catalysis oxidizing method should be studying and improving further the manufacturing technology, and developing new catalysts and catalyst promoters which are high effective and nonpoisonous.
2 Manufacture of PFS with slag or waste residue
It is a good method of turning waste into useful product to manufacture PFS from slag or waste residue containing oxide compound of iron. It can not only solve the three-waste problem, and also cut down the cost of PFS, simplify manufacturing technology, have better economic benefit.
2.1 Manufacture of PFS with pyrite cinder
Pyrite cinder can be as a raw material of PFS. This is one of major methods preparing PFS with slag or waste residue. A vast amount of pyrite cinder is produced in the producing course of sulfuric acid. Its main components are ferric oxide and ferriferrous oxide. At the aspect of the comprehensive utilization of pyrite cinder, the greater part of pyride cinder was used as an assistant in the production of cement.
In general situation, total iron content is about 65~65% in pyrite cinder and ferric content is 96.5% in total iron. After pyrite cinder is dissolved in sulfuric acid, the filtrating can directly be used in the manufacture of PFS. This has developed another better way for the comprehensive utilization of pyrite cinder. The manufacturing method of PFS using pyrite cinder is economical, and its cost is also lower. At present, many progresses had been made in this aspect[19-22].
The manufacturing process of PFS using pyrite cinder may be divided into two steps. The first step is that pyrite cinder is dissolved in sulfuric acid:
Fe3O4 + 4H2SO4 = Fe2(SO4)3 + FeSO4 + 4H2O (18)
Fe2O3 + 3H2SO4 = Fe2(SO4)3 + 3H2O (19)
The second is oxidation, hydrolysis and polymerization:
FeSO4＋2H2SO4＋O2 ＝ 2Fe2(SO4)3＋2H2O (20)
Fe2(SO4)3 + nH2O ＝ Fe2(OH)n(SO4)3-n/2 + (n-2)H2SO4 (21)
mFe2(OH)n(SO4)3-n/2 ＝ [Fe2(OH)n(SO4)3-n/2]m (22)
In the second step, ferrous sulfate may be oxidized with different methods. One is directed oxidation[19]. Another is catalysis oxidation[41]. Moreover, when the content of ferrous sulfate is very low in the filtrating, the oxidation may be left out and both the hydrolysis and polymerization can take place directly[21,22].
In the manufacturing process, it is important to improve the dissolving rate of pyrite cinder furtherly in sulfuric acid. Author's studies indicated[23,24] that the dissolving rate is concerned with sulfuric acid concentration, temperature, and the ratio between solid and liquid. Because the dissolving course of pyrite cinder is an exothermic reaction, the dissolving rate may achieve 95% under the effect of the reaction heat. The content of ferrous only occupies 3% of the total iron content in the filtrating. PFS can be obtained through the hydrolyzing and the polymerizing of ferric sulfate under certain condition. Oxidizer is not needed in the manufacturing process. This has not only eliminated the pollution of nitric oxides, and also saved spending and cut down further the cost of product.
When PFS made by ourselves was used in the treatment of papermaking waste water (CODCr = 1000mg/L), the removal rate of CODCr was more than 90% as the addition of PFS was 150mg/L(that is, [Fe3+]=150mg/L). In addition, the removal rate of CODCr was more than 60% in the treatment of saccharin sodium slat waste water(CODCr = 15000mg/l) as the addition of the PFS was 800mg/L.
In order to raise the dissolving rate furtherly, pyrite cinder may be preprocessed. First, ferric oxide in pyrite cinder was reduced as ferrous oxide under the effects of both high temperature and reducer. Pyrite cinder was changed into reduction dregs. Second, the reduction dregs was dissolved in sulfuric acid, obtaining mid-product ferrous sulfate. Final, PFS was made through oxidation and hydrolysis and polymerization as mentioned in 1.2.
It was said that this method can raise the utilization ratio of pyrite cinder, nevertheless there was not only oxidizing reaction but also reducing reaction in the manufacturing process of PFS. So it will result in longer producing period and higher consumption, and its popularization and application will be very difficult, too.
2.2 Manufacture of PFS with other slags containing iron
Siderite, magnetite ore, iron mud, natural iron sand and open-hearth furnace dust[25-28] are also the raw materials of PFS besides pyrite cinder. The contents of ferriferrous oxide and ferric oxide are high in them, too.
Literature [26] had obtained better result in the manufacture of PFS using iron mud. Iron mud is the waste produced in the producing process of dye mediums. Its main component are ferriferrous oxide and a little ferric oxide, ferrous oxide, and iron besides. In China, the treatment method of iron mud is generally to store up or to bury. This causes easily environmental pollution again, and the useful resource in iron mud is also wasted. It is a good way of waste comprehensive utilization for iron mud to be used as the raw material of PFS.
Natural iron sand is a kind of rich mineral resources of the Dabieshan Mountains area. Total iron content is 59.6% in it, and ferric content is 41.1%. It is a good raw material of preparing PFS. Literature [27] reported, using natural iron sand and sulfuric acid as the raw materials, high concentration PFS(220g/L) could be made through pickling, oxidizing, and polymerizing. Then , the liquid PFS was concentrated into solid by spray-drying process.
Open-hearth furnace dust is another waste used also to manufacture PFS. It is the smoke and dirt in the open-hearth furnace steelmaking waste gas. The content of ferric oxide is more than 90% in it. Literature [28] reported that the dust could be used as the raw material of PFS: Firstly, the dust was dissolved in alkali solution for removing some impurity in it. The content of ferric oxide was more than 99.5% in the dust purified. Then PFS could be made through acid dissolving, hydrolysis and polymerization. When the PFS was used to treat washing waste water of blast furnace gas, the treated efficiency was very good. Moreover, because there is not other harmful ion in the PFS, it is very suitable for the PFS to treat drinking water.
In other reports, waste residue containing ferric oxide was used to manufacturing PFS, too. Under certain temperature and pressure, PFS could be obtained by dissolving, hydrolysis, polymerization without oxidizer.
On the whole, the manufacture of PFS by slags or waste residue is an economical method. This method is simpler than the catalysis oxidation method mentioned above. Certainly, there are still some problems that should be solved furtherly in the manufacturing process of PFS. For example, the dissolving rate of slags should be raised again, so as to raise the utilization rate of raw material. In addition, there is excessive acid generally in the solution of ferric sulfate obtained by dissolving slags in sulfuric acid. This will increase the consumption quantity of other assistants in the course of hydrolysis and polymerization. If there are some harmful heavy metals in slags and waste residue, there will be some heavy metal ions in PFS. This will restrict its application in drinking water treatment.
3 Manufacture of PFS with other methods
3.1 Method of biologic oxidation
Using pyrite, coal, sulfur, and hydrogen sulfide as raw materials, PFS can be made with the method of biologic catalyzing oxidation under the influence of iron-sulphur bacteria, such as thiobacillus ferrooxidans and thiobacillus thiooxidans. Literature [29] investigated some factors which affecting the manufacturing of PFS with biologic oxidation. It reported that these factors were pH, the addition of pyrite, temperature, stirring, and reaction time. Under the conditions of pH2.0~2.3, 2.8g pyrite/L, 30℃, and 300 r.p.m., a mid-product was obtained in 10 hours reaction. Then PXT coagulant(that is PFS) was made through acidification, concentration, and aging. When the PXT was used to treat the high SS ash water of power plant, it could decrease not only SS but pH and F-.
In the process of biologic oxidation, both thiobacillus ferrooxidans and thiobacillus thiooxidans play an important role. They are the peculiar micro-organisms which can obtain carbon resources from CO2 in air and live in inorganic environment. They can oxidize iron and reduce sulphur into ferric and sulfuric acid, respectively.
The preparation of PFS with biologic oxidation is a very good way. The way does not need any other raw materials besides pyrite and a little dilute sulfuric acid used to adjust the pH of reaction system. It is characterized by simple proces, saving energy. Nevertheless, many studies should be done if the method of biologic oxidation is used in industrial production of PFS. At present, this method is still in the initial stage of study and development.
3.2 Method of electrolytic oxidation
It should be pointed out that the electrolytic oxidation of ferrous sulfate is also a preparing methods of PFS. First, ferrous sulfate was oxidized into ferric sulfate with D.C. electricity in electrolytic bath. Then , PFS was obtained through the hydrolysis and the polymerization of sulfate ferric. However, the electrolytic oxidation expends enormous electric energy. It can not be spreaded and applied in industry.
4 Manufacture of solid PFS
In general, the product of PFS is liquid state. This product has the merit of being easy to use in waste water treatment process, but its shortcoming is that the cost of transportation is higher than solid state because of its valid component lower than solid. So some studies about the manufacture of solid PFS had been made.
Solid product had been developed though concentrating liquid PFS[9,12,15,27], such as heating evaporization, stoving, and vacuum evaporation and drying. We call these methods the two-step process as it includes both the preparation of liquid PFS and the concentration.
Kreplka J[30,31] reported that solid PFS could be manufactured by oxidizing the solution of ferrous sulfate with air under the conditions of 120~180℃ and 0.3~2.5 MPa. In addition, Prasak T P[32] developed a simple method of manufacturing solid PFS: firstly, preparing solid basic ferric sulfate by oxidating ferrous sulfate with air in a revolving blast furnace under the conditions of 200℃ and 3 hours, and then obtaining solid PFS by making the solid basic ferric sulfate reacts with sulfuric acid. The shortcoming of the method is that the oxidation of ferrous sulfate is not complete in the first step. Using solid raw materials, Li Kechang[33] also succeeded in manufacturing solid PFS through solid phase reaction.
Recently, Wang Duoren[34] reported that solid PFS could also be made by one-step process. First, mixturing the solution of potassium chlorate and the suspension of ferrous sulfate. Then, obtaining solid granulated PFS under the conditions of 100℃and pH2-3 after 1 hour reaction.
Although having overcome the shortcoming of the high transportation cost of liquid PFS, solid PFS consumes enormous heat energy in manufacture process, and it have to be dissolved again before being used in flocculation process. So the suitable method of manufacturing PFS should be to make high concentration liquid PFS.
5 Stability of PFS
If liquid PFS is long-term stored, Fe(OH)SO4 sediment will be produced in PFS solution, that is, liquid PFS is unstable. The stability of PFS is a very universal and very important problem, and it must be considered in the manufacture and the application of PFS, but this problem is reported seldom in most literatures about PFS.
Liu Changrang et al.[9] had studied the stability of PFS and pointed out that liquid PFS, which was made from ferrous sulfate with catalysis oxidation method, was unstable. One stabilizer was added in liquid PFS in order to strengthen the stability of PFS. In addition, Shu Wangen et al.[35] and Wang Shicai et al.[36] had studied the stability of polymerized ferric chloride and polymerized aluminum sulfate, respectively. Their experimental results shown that stable polymerized ferric chloride could be made by adding stabilizer S-3 in solution, and tartaric acid was a good stabilizer of polymerized aluminum sulfate.
Author's studies indicate that liquid PFS made with other methods also has the instability. The stability of PFS is related to the PH of solution and the concentration of SO42- in solution. So, besides adding some stabilizers in PFS, both adjusting the pH and controlling the concentration of SO42- are a effective method, too.
Finally, it should be pointed out that changing liquid PFS into solid through evaporation and drying is a good way of solving the instability of liquid PFS.
6 Conclusion
Comparing with other coagulants, PFS is the best kind of inorganic water treatment agents and doesn’t produce twice pollution. It has a wide application prospect. The catalysis oxidizing method of ferrous sulfate had been popularized and applied in industrial production. It is a major manufacturing method of PFS at present. However, there are still some problems which should be solved in manufacturing process. Besides, the manufacturing methods of PFS with pyrite cinder and other slags are the good way of economy, saving energy, and no twice pollution. It has a very good popularization and application prospect and market competition power. For the method of biologic oxidation, it is still in the initial stage of study and development. It should be developed and improved further before being applied in industrial production.
Acknowlegment
We thank the Scientific and Technical Committees of Henan Province (001200220, 991190306) and The Key Laboratory of Environmental Science and Engineering of Henan Province for financial support.
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中文摘要：
无机高分子聚合铁盐类混凝剂制备方法评述
李明玉
（暨南大学环境工程系, 广州 510632, liming-yu@sohu.com）
摘要 综述了无机高分子聚合铁盐类混凝剂的几种生产制备方法。对用硫酸亚铁经催化氧化法和直接氧化法制备聚合硫酸铁，用各种含铁工业废渣制备复合聚铁，以及采用生物和电化学方法制备聚铁类混凝剂等方法的优缺点等作了较全面评述。还对固体聚合铁的生产及液体聚合铁混凝剂的稳定性进行了讨论，对目前聚合铁生产中存在的问题及发展方向提出了建议。
关键词 聚合硫酸铁 硫酸亚铁 混凝剂 硫铁矿烧渣
基金项目：河南省科技攻关项目(001200220,991190306)、河南省环境科学重点开放实验室资助课题
第一作者及联系人: 李明玉, 男, 39岁, 博士, 教授. 主要从事污染防治工程与技术、水处理药剂研究等方面的工作。完成和承担省部级项目10项, 发表学术论文40余篇.