A yellow iron sputum method of iron removal a precipitate composition and thermodynamic stability of scutellaria scutellaria The molecular formula of scutellaria can usually be written as A 2 0·3Fe 2 0 3 ·4S0 3 ·6H 2 0 or AFe 3 (S0 4 ) 2 ( OH) 6 , or A 2 [Fe 6 ( SO 4 ) 4 (OH) 12 , wherein A represents a monovalent cation, ie may be K + , Na + , NH 4 + , Rb + , Ag + , —Pb 2 + or H 3 + O, etc., for example: The equilibrium solid phase is the hydrate of iron oxide. This is a very narrow area, located in the leftmost triangle 1 in the figure. In this region, the solid phase precipitated from the liquid phase is iron oxide monohydrate or iron oxide trihydrate. Since the latter is a metastable phase rather than an equilibrium phase, it is not marked on the graph. The liquidus phase does not substantially intersect the Fe 2 0 3 -S0 3 binary system edge, and thus the degree of hydrolysis of the iron oxide hydrate in water is very small. The triangle 1 is far from the component S0 3 , indicating that the acidity of the system is very low, and the high iron is precipitated from the cast in the form of ferric hydroxide and goethite. The removal of iron from the yellow iron shovel must deviate from this area, that is, the solution must be kept at a certain acidity. [next] c Effect of solution acidity on precipitation The pH value of the solution has an important influence on the stability and precipitation rate of the yellow iron samarium. Yellow iron strontium produces a large amount of acid during the formation process, and an increase in acidity will reduce the amount and rate of iron precipitation. The relationship between the concentration of Fe 3+ in the mother liquor and the concentration of sulfuric acid is theoretically C Fe 3+ /C H2SO4 = 0.004, but the above ratio is often taken as 0.01 in factory operation. The temperature-pH relationship has been studied, as shown in the right figure above. The shaded part of the figure is the area where the yellow shovel is stable. It indicates that at low pH, pyrite must be stable at higher temperatures: at 20 °C, the pH range is 2 to 3; at 100 °C, the pH range is 1 to 2.3; and at 200 °C, The pH is from 0 to 1.2. In fact, the pH is less than 0.6, the solution potential is greater than 0.60V, and the Fe 3+ concentration is greater than 0.001 mol/dm 3 , and the yellow iron sputum can be stably present. The figure below shows the plot of potential versus pH. It indicates that the yellow iron sputum is stable in the range of pH = 0.5 to 2.5. [next] d Effect of reaction temperature on precipitation The formation of yellow iron sputum at room temperature is very slow. For example, in the K 2 S0 4 -Fe 2 (S0 4 ) 3 solution, the potassium ferrite is precipitated at 25 ° C, and the pH of the aqueous phase is in the range of 0.82 to 1.72, and it takes 1 to 6 months. If the temperature is raised to 100 ° C, the precipitation is nearly complete after a few hours; if the temperature reaches 180 ~ 200 ° C, jarosite begins to destroy. 43 Tv Case,Generoustelevision Case,Flat Screen Television Case,Tv Protective Case Jiangsu Hengye Precision Technology Co.,Ltd , https://www.hdigitaltv.com
Potassium sulphate: KFe 3 (S0 4 ) 2 (OH) 6 , its chemical composition: K 2 0 9.41%, Fe 2 0 3 47.83%, S0 3 31.97%, H 2 0 10.79%. Yellow sodium iron strontium: NaFe 3 (S0 4 ) 2 (OH) 6 , its chemical composition: Na 2 0 6.4%; Fe 2 0 3 49.42%; S0 3 33.04%, H 2 0 11.14%. Yellow ammonium iron samarium: NH 4 Fe 3 (S0 4 ) 2 (OH) 6 , its chemical composition: (NH 4 ) 2 O 5.43%, Fe 2 0 3 49.93%, S0 3 33.37%, H 2 0 11.27%.
These compounds are commonly referred to as jarosite or pyrite. In nature, some minerals have a similar composition, the same structure and crystalline form, the so-called isomorphism. The so-called cockroach is a general term for a series of isomorphous minerals, and jarosite is one of the cockroaches.
Bobei Zneike and Melvin studied the equilibrium of the Fe 2 0 3 -S0 3 -H 2 0 ternary system at certain temperatures, as shown in the following figure. All basic, acid and normal salts are located inside the ternary phase diagram because they all contain crystal water. The anhydrous ferric sulfate is located on the Fe 2 0 3 -S0 3 binary line, but it is not in the equilibrium phase at 50 ° C and 75 ° C, ie it will not be analyzed from this solution in the solution, so it is not in the figure. Appeared on. Classified according to the equilibrium solid phase, the map can be roughly divided into the following three types of areas: 
The equilibrium solid phase is a mixture of a basic salt or a basic salt and an iron oxide hydrate. The triangles 2-7 belong to such regions, which are composed of a liquid phase and a solid phase. It can be seen that the equilibrium solid phase of the triangle 2 is a hydrate of iron oxide and a ferric sulphate salt containing crystal water (3Fe 2 0 3 ·4S0 3 ·9H 2 0). In 3-7, the equilibrium solid phase is It is one or two different basic salts.
The equilibrium solid phase is a normal salt, an acid salt or a mixture thereof. The triangular region 9-13 belongs to such a region, and an increase in S0 3 % in the system causes a sharp drop in the equilibrium liquidus, that is, the iron content of the mother liquor. These areas are characterized by a balanced liquidus line containing a high S0 3 %. Directly related to the iron iron of the yellow iron shovel is the zone 2-3, and their corresponding stable equilibrium solid phase is the basic salt yellow sorghum 3 Fe 2 0 3 · 4S0 3 · 9H 2 0, can also be written as [H ( H 2 0)] 2 0·3 Fe 2 0 3 · 4S0 3 · 6H 2 0, which is very similar to jarosite in terms of composition or physicochemical properties. Therefore, when K + , Na + , NH 4 + are present in the solution, the equilibrium solid phase will be replaced by a more stable pyrite. As the acidity of the solution decreases, the yellow iron tendon tends to be unstable and will be converted into aqueous iron oxide. In order for the high iron to precipitate as iron, it is necessary to keep the solution at a certain acidity.
The reaction for precipitating iron slag from iron sulphate solution is as follows:
3Fe 2 (S0 4 ) 3 +6H 2 O ==== 6Fe(OH)S0 4 +3H 2 S0 4
4Fe(OH)S0 4 +4H 2 0 ==== 2Fe 2 (OH) 4 S0 4 +2H 2 S0 4
2Fe(OH)S0 4 +2Fe 2 (OH) 4 S0 4 +2NH 4 0H ====(NH 4 ) 2 Fe 6 (S0 4 ) 4 (OH) 12
2Fe(OH)S0 4 +2Fe 2 (OH) 4 S0 4 +Na 2 S0 4 +2H 2 0 ==== Na 2 Fe 6 (S0 4 ) 4 (OH) 12 +H 2 SO 4
2Fe(OH)S0 4 +2Fe 2 (OH) 4 S0 4 +4H 2 0 ====(H 3 0) 2 Fe 6 (S0 4 ) 4 (OH) 12
When the yellow iron sputum is formed, sulfuric acid is produced. The acid must be neutralized and the reaction can continue. Calcination is usually used as a neutralizing agent in zinc smelting. In other cases, Fe 2 O 3 , Na 2 C0 3 or the like may be used as a neutralizing agent.
The formation of the crystals of the yellow stellate requires Fe 3+ , and the actual industrial filtrate contains Fe 2+ in different proportions. Therefore, the oxidation of Fe 2+ into Fe 3+ is the first step before crystallization. The oxidizing agents are KMn0 4 , Mn0 2 , C1 2 , NaC1O 3 and peroxo sulfide. In the practice of the wet zinc smelting industry, 0 2 or air is used as the oxidant. The speed of indulgence is an important issue that people pay attention to. Ma Rongjun of Changsha Research Institute of Mining and Metallurgy has made systematic work on dynamics.
b Effect of monovalent cations on crystallization The condition of the formation of stellate is that Na + , K + or NH 4 + plasma must be present in the solution. Commonly used compounds are NH 4 0H, (NH 4 ) 2 S0 4 , NH 4 HC0 3 , Na0H, Na 2 S0 4 and KC1 and the like. The amount of monovalent ions to be added must satisfy the atomic ratio specified by the chemical formula AFe 3 (OH) 6 , that is, Fe/A must be equal to or greater than 3 to obtain a good iron removal effect. The iron removal effect of different kinds and amounts of monovalent cations is shown in the figure below. As can be seen from the figure, the potassium ion effect is the best, and the effect of sodium and ammonium ions is close. [next]
The operating temperature requirement for sinking is higher than 85 ° C, and the effect of temperature on the precipitation results is shown in the right figure above. The low temperature is not only slow to precipitate but also difficult to filter. The solubility of scutellaria in acidic media decreases sharply with increasing temperature.