Technology for preparing polysilicon ferric sulfate sulphate from hematite

Poly ferric sulfate, silicon chloride (PSFCS) is a highly complex inorganic polymer coagulant, the metal ions are introduced into the active silicic acid prepared composite coagulant obtained. Hematite is an iron oxide ore. It is difficult to sort. The main useful chemical components are Fe ₂ O ₃ and a small amount of FeO. If the iron content is required to meet the requirements of ironmaking, the cost of ore dressing is often higher. high. Based on the increasing demand for coagulants, the use of low-grade hematite for the synthesis of coagulants is a worthwhile approach. No relevant reports have been found yet.

First, the experimental method

(1) Main instruments and raw materials

DBJ-621 six-time timing variable speed mixer for timing and constant speed mixing; 79HW-1 type constant temperature magnetic stirrer for temperature regulation and stirring; WG2-200 type scattering turbidity meter for measuring turbidity; pHS-3C pH meter, for measuring the pH; elution hematite Fe ^{3 +} concentration, reduction using stannous chloride, sodium diphenylamine sulfonate as indicator weight chromium potassium titration. The COD was determined by the potassium dichromate method.

Hematite is taken from an iron ore mine in Jiangsu [w(Fe)=55%]; hydrochloric acid is chemically pure [w(HCL)=37%]; sulfuric acid is industrial product [w(H ₂ SO ₄ )=98%]; Sodium silicate is an industrial product [w(SiO ₂ ) = 26%, modulus 3.1, ρ = 1.36 kg/L]. Potassium dihydrogen phosphate, and sodium nitrite is chemically pure. The experimental water is tap water. The wastewater was taken from a printing and dyeing factory in Jiangsu Province. The wastewater quality was COD _Cr of 316.8 mg/L, turbidity of 144.4 NTU and pH of 9.0. The components were mainly active fuel and black in color.

Raw ore properties: The main metal mineral in the ore is hematite, followed by magnetite and limonite. The hematite inlay has a fine grain size. The magnetite is mainly in the form of self-formed grains. The size of the inlaid cloth is coarse and is replaced by hematite. It is often filled with hematite in the gangue mineral cracks. The main limonite is It is formed by oxidative alteration of hematite and basically retains the embedding characteristics of the original hematite. The gangue mineral is mainly composed of quartz and contains a small amount of mica , garnet , chlorite and the like. Its structure is coarse-grained grain-like structure and contact-filling cementation. The sand composition is mainly quartz, followed by magnetite. It is filled with a small amount of garnet and chlorite. The garnet is self-shaped. Granular, closely associated with iron minerals, produced as cement.

The main chemical composition analysis results of the concentrate are listed in Table 1. The mineral powder has a particle size of less than 0.1 mm, and the iron mineral is mainly a monomer and a continuous body.

Table 1 Analysis results of main chemical components of concentrates (mass fraction) /%

(2) Preparation of PSFCS coagulant

Take a certain amount of hematite powder, add appropriate amount of mixed acid at different concentrations, control the liquid-solid ratio of 3.0-4.5, heat and stir at 80-110 °C, add appropriate amount of stabilizer KH ₂ PO ₄ and catalyst NaNO ₂ respectively during heating. Oxygen oxidation is carried out, and after cooling, filtration is carried out to obtain a polychlorinated ferric sulfate solution. Dilute hydrochloric acid to 3~6mol/L, dilute sulfuric acid to 6~12mol/L, and then mix 1:1; take two-stage countercurrent cascade, ie two-stage leaching; one leaching solution enters two sections and fresh red iron The ore is mixed, and the second-stage filter residue is mixed with a fresh mixed acid. One leaching time is 1 to 2.5 h, and the second leaching time is 1 h. KH ₂ PO _{4 was} added to one stage, and NaNO _{2 was} added to the second stage.

Dissolve a certain amount of sodium silicate into water, prepare a sodium silicate solution of 130-150mg/L, adjust the pH value with dilute sulfuric acid, control pH=2, activate at room temperature for a certain period of time, and then add hematite. The prepared polyferric chloride sulphate solution is aged for about 2 hours to obtain a PSFCS coagulant.

(3) Treatment of printing and dyeing wastewater with PSFCS

Add 100mL of water sample to the beaker first, then add a certain amount of coagulant PSFCS, and use DBJ-621 type variable speed mixer to stir at 160r/min for 2min, so that the coagulant is fully dispersed in the wastewater and then reduced. The rotation speed was 40r/min, stirred for 10min, then transferred to a 100mL measuring cylinder. After standing for 20 minutes, the clarification liquid of 25 mm from the liquid surface was taken to analyze the turbidity and COD _{Cr of the} water.

Second, the experimental results and discussion

(1) Preparation conditions of polychlorinated ferric sulfate solution

The experiment used partial orthogonal experimental design. Through the exploration experiment, four influencing factors and the scope of examination were determined in advance. The acid leaching temperature is 80-110 ° C, the sulfuric acid concentration is 3-6 mol/L, the hydrochloric acid concentration is 1.5-3 mol/L, the acid leaching time is 2-3.5 h (sum of 1, 2), and the liquid-solid ratio is 3:1. ~4.5:1. The orthogonal table L ₁₆ (4 ⁵ ) is selected, and each factor is tested for 4 levels. The factors and levels are shown in Table 2. The orthogonal experimental results are shown in Table 3. The fifth column in the table is a blank column for estimating the experimental error and variance. Analysis, analysis of variance results are shown in Table 4. The statistical average of the iron leaching rate under various factors is shown in Figure 1.

Table 2 Orthogonal experimental factors and levels of iron leaching rate

Table 3 Orthogonal experimental results of iron leaching rate

Table 4 Analysis of variance of iron leaching rate

Figure 1 Iron leaching rate orthogonal experimental results k-value map

According to the change trend of the k value of the orthogonal experiment results in Fig. 1, it can be seen that the iron leaching rate is the highest when the four influencing factors are all four levels. For the A factor (acid leaching temperature), the temperature rise is beneficial to accelerate the dissolution rate of iron, and contribute to hydrolysis and polymerization. Based on the mixed acid leaching, the concentration of the single acid is low, it is not volatile, and the temperature can be taken. Therefore, the A factor is set to 4 levels, that is, the acid immersion temperature is 110 ° C. As the acid concentration (B factor) increases, the iron leaching rate increases, but when the concentration is greater than 3, the iron leaching rate increases. Therefore, the B factor is set to 3 levels, that is, the sulfuric acid concentration is 5 mol/L, and the hydrochloric acid concentration is 2.5 mol/L. The leaching rate of iron is directly proportional to the C factor (acid leaching time), but the leaching time contributes less to the leaching rate, so the C factor is set to 3 levels, that is, the acid leaching time is taken for 3 hours. As the D factor (liquid-solid ratio) increases, the iron leaching rate increases. Because the liquid-solid ratio increases, the liquid-solid contact area of ​​the reaction increases, but at the same time, it means that the acid excess coefficient increases, and the iron leaching rate increases, which causes the base degree to decrease, resulting in the alkalization degree of the product. Lowering; in addition, it will cause an increase in acid consumption, an increase in free acid in the product, and an increase in cost, so the D factor is set at 3 levels. That is, the liquid-solid ratio is 4.

According to the above analysis, the optimum level is A ₄ B ₃ C ₃ D ₃ . Two sets of verification experiments were arranged at the optimal level, and the leaching rates of iron were 95.1% and 94.3%, respectively.

(II) Preparation of polysilicon silicate sulphate and its effect on wastewater treatment

Firstly, according to the exploratory experiment, the range of investigation of each influencing factor is determined: the pH value of silicic acid activation is 1-4, the molar ratio of Fe/Si is 1-4, the activation time of silicic acid is 20-50 min, and the aging time is 1.5-3 h. . The orthogonal table L ₁₆ (4 ⁵ ) is selected, and each factor is tested for 4 levels. The factors and levels are shown in Table 5. The results of the orthogonal experiment are shown in Table 6. The fifth column in the table is a blank column, and the amount of PSFCS added to the wastewater is 100 mg/L. The results of the analysis of variance are shown in Tables 7 and 8. The statistical average values ​​of turbidity removal rate and COD removal rate under different factors are shown in Fig. 2 and Fig. 3, respectively.

Table 5 Orthogonal experimental factors and levels of synthesis conditions

Table 6 Orthogonal experimental results of synthesis conditions

Table 7 Analysis of variance of turbidity removal rate

Table 8 Analysis of variance of COD removal rate

Figure 2 Synthesis conditions and turbidity removal rate orthogonal experimental results k-value map

Figure 3 Synthetic conditions and COD removal rate orthogonal experimental results k-value map

From the trend of the k value of the orthogonal experiment results in Fig. 2 and Fig. 3, it can be seen that with the increase of the A factor (silic acid activation pH value) or the B factor (Fe/Si molar ratio), the turbidity and The removal rate of COD _Cr increased, but after level 2, the removal rates of turbidity and COD _Cr decreased. Therefore, the optimum silicic acid activation pH and Fe/Si molar ratio are both at level 2. Factor C (silicic acid activation time) and D factors (aging time) is the highest turbidity COD _Cr and 4 removal level, but more than two levels of turbidity and COD _Cr removal rate trends, it was 2 ~ 3 levels are suitable, that is, the activation time of silicic acid is controlled at 30 to 40 minutes, and the aging time is controlled at 2 to 2.5 hours.

Third, the conclusion

The inorganic polymer coagulant PSFCS was prepared by using hematite, hydrochloric acid, sulfuric acid and sodium silicate as raw materials. The suitable process conditions for preparing inorganic polymer coagulant PSFCS are: sulfuric acid concentration 5mol/L, hydrochloric acid concentration 2.5mol/L, liquid-solid ratio 4:1 (mass ratio), acid immersion temperature 110°C, acid leaching time 3h The pH value of silicic acid activation is 2, the molar ratio of Fe/Si is 2, the activation time of silicic acid is 30-40 min, and the aging time is 2 to 2.5 h. The PSFCS coagulant has good flocculation performance and can effectively remove the turbidity and COD _{Cr of} printing and dyeing wastewater. The highest removal rates are 95.5% and 80.2%, respectively.