Method of preparing inorganic macromolecular flocculant by polymerizing silicate and zirconium chloride

Abstract

A method for preparing inorganic macromolecular flocculant by polymerizing silicate and zirconium tetrachloride is disclosed and relates to the field of feed water treatment. The invention aims at the problem of poor efficiency of inorganic low-molecular zirconium salt flocculant in treating low-temperature raw water and blockage of flocculation, by copolymerization of polymeric zirconium chloride and polysilicic acid, the Si—O—Zr bond was formed to increase the molecular chain of the flocculant to strengthen the function of adsorption bridge and net capture sweep. Under low temperature, the flocculant can remove organic pollutants effectively, and the size of flocs formed is large and easy to precipitate. The invention is particularly suitable for the treatment of raw water at low temperature, low turbidity and high organics by enhanced coagulation.

Claims

1. A method for preparing an inorganic macromolecular polysilicic acid and poly-zirconium chloride flocculant, wherein starting materials used for the preparation comprises sodium silicate, zirconium tetrachloride, sodium hydroxide, and sulfuric acid, comprising the steps of: (1) weighing the starting materials and preparing solutions of each of the starting materials; (2) adding the sodium silicate solution to 0.2˜0.3 mol/L sulfuric acid solution dropwise, continuously stirring at 500˜600 rpm at 20˜25° C., maintaining pH under 2 for the mixture of the sodium silicate solution and sulfuric acid solution, curing by resting for 3˜4 hours to yield a polysilicic acid solution; (3) adding the sodium hydroxide solution to the zirconium tetrachloride solution dropwise, continuously stirring at 500˜600 rpm at 20-25° C. until the mixture of the sodium hydroxide solution and the zirconium tetrachloride solution becomes colorless and transparent, curing by resting for 3˜4 hours to yield a poly-zirconium chloride solution with alkalization degree (B) of 0.5˜2.0; (4) measuring out appropriate amount of the polysilicic acid solution at a level that keeps molar ratio of zirconium/silicon in a range of 5˜20, adding the polysilicic acid solution dropwise to the poly-zirconium chloride solution under continuous stirring at 500˜600 rpm at 20˜25° C., continuing to stir at 500˜600 rpm at 20˜25° C. for 5˜6 hours, curing by resting for 20˜24 hours to yield the inorganic macromolecular polysilicic acid and poly-zirconium chloride flocculant.

2. The method for preparing the inorganic macromolecular polysilicic acid and poly-zirconium chloride flocculant according to claim 1, wherein a concentration of the polysilicic acid solution in step (2) is 0.08˜0.12 mol/L.

3. The method for preparing the inorganic macromolecular polysilicic acid and poly-zirconium chloride flocculant according to claim 1, wherein a concentration of the poly-zirconium chloride solution in step (3) is 0.2˜0.3 mol/L.

4. The method for preparing the inorganic macromolecular polysilicic acid and poly-zirconium chloride flocculant according to claim 1, wherein the molar ratio of zirconium/silicon is 5˜10:1 when a temperature of treated water is under 5° C., and 10˜20:1 when the temperature of treated water is between 5° C.˜10° C.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment I

(1) Water from a river in Beijing was taken as raw water for testing. The turbidity of the raw water was 21.8 NTU, Dissolved Organic Carbon (DOC) was 12.3 mg/L, pH was 7.3, and water temperature was 8.8° C.

(2) The flocculant prepared by the method of the invention was used to perform coagulation test on the river water, the process being: the flocculant was added at the beginning of the coagulation test with rapid stirring at 500 RPM for 1 minute, followed by stirring at a slow rate of 50 RPM for 15 minutes, and water quality was measured after 15 minutes of static precipitation.

(3) When the temperature of treated water is within 5˜10° C., the molar ratio of Zirconium/Silicon was selected at 10˜20:1 for preparing inorganic macromolecular polysilicic acid and poly-zirconium chloride flocculant, the specific preparation process is as follows:

(4) (1) Weigh 7.4039 g solid Na.sub.2SiO.sub.3.9H.sub.2O and dissolve it in 50 mL deionized water and add into 0.2 mol/L dilute sulfuric acid solution drop by drop via an injection pump at the rate of 0.1 ml/min accompanied with continuous stirring at 550 rpm and 25° C., the pH value of the mixture during the reaction process is controlled at 1.5 by 0.6 mol/L dilute sulphuric acid, cure by resting for 3 hours, 0.1 mol/L polysilicic acid solution was obtained in a volumetric flask with a capacity of 250 mL;

(5) (2) Using an injection pump to add 50 ml 0.4 mol/L NaOH solution into 50 ml 0.4 mol/L zirconium tetrachloride solution drop by drop at the rate of 0.1 mL/min, the process was carried out at 25° C. with continuous stirring at 550 rpm until the solution was colorless and transparent, cure by resting for 3 hours, 0.2 mol/L poly-zirconium chloride solution with alkalinity (B) of 1.0 was obtained;

(6) (3) Using an injection pump to add 20 ml the 0.1 mol/L polysilicic acid solution into 100 ml 0.2 mol/L poly-zirconium chloride solution drop by drop at the rate of 0.05 mL/min, the process was carried out at 25° C. with continuous stirring at 550 rpm, continue stirring at 550 rpm at 25° C. for 6 hours after the titration, cure by resting for 20 hours, and collect the inorganic macromolecular polysilicic acid and poly-zirconium chloride flocculant with 10:1 molar ratio of Zirconium/Silicon.

(7) The test results are shown in Table I:

(8) TABLE-US-00001 Turbidity of Precipitated Dosage (In precipitated water DOC Reagent zirconium, mM) water (NTU) (mg/L) Zirconium 0.8 1.6 2.7 tetrachloride Polymerizing 0.5 1.8 2.2 silicate and zirconium chloride

(9) Compared to using zirconium tetrachloride alone, the inorganic macromolecular polysilicic acid and poly-zirconium chloride flocculant with 10:1 molar ratio of Zirconium/Silicon exhibited the comparable removal rate for turbidity and organics, despite a 37.5% reduction in input (in zirconium), the method disclosed in this application is proven to be effective in the treatment of low temperature raw water.

Embodiment II

(10) Water from a lake in a park in Beijing was taken on a November as raw water for testing. The turbidity of the raw water was 6.6 NTU, DOC was 6.3 mg/L, pH was 7.5, and water temperature was 3.2° C.

(11) The flocculant prepared by the method of the invention was used to perform coagulation test on the river water, the process being: the flocculant was added at the beginning of the coagulation test with rapid stirring at 500 RPM for 1 minute, followed by stirring at a slow rate of 50 RPM for 15 minutes, and water quality was measured after 15 minutes of static precipitation.

(12) When the temperature of treated water is within <5° C., the molar ratio of Zirconium/Silicon was selected at 5˜10:1 for preparing the inorganic macromolecular polysilicic acid and poly-zirconium chloride flocculant, the specific preparation process is as follows:

(13) (1) Weigh 7.4039 g solid Na.sub.2SiO.sub.3.9H.sub.2O and dissolve it in 50 mL deionized water and add into 0.2 mol/L dilute sulfuric acid solution drop by drop via an injection pump at the rate of 0.1 ml/min accompanied with continuous stirring at 550 rpm and 25° C., the pH value of the mixture during the reaction process is controlled at 1.5 by 0.6 mol/L dilute sulphuric acid, cure by resting for 3.5 hours, 0.1 mol/L polysilicic acid solution was obtained in a volumetric flask with a capacity of 250 mL;

(14) (2) Using an injection pump to add 50 ml 0.4 mol/L NaOH solution into 50 ml 0.4 mol/L zirconium tetrachloride solution drop by drop at the rate of 0.1 mL/min, the process was carried out at 25° C. with continuous stirring at 600 rpm until the solution was colorless and transparent, cure by resting for 3.5 hours, 0.2 mol/L poly-zirconium chloride solution with alkalinity (B) of 1.0 was obtained;

(15) (3) Using an injection pump to add 40 ml the 0.1 mol/L polysilicic acid solution into 100 ml 0.2 mol/L poly-zirconium chloride solution drop by drop at the rate of 0.05 mL/min, the process was carried out at 25° C. with continuous stirring at 600 rpm, continue stirring at 600 rpm at 25° C. for 5 hours after the titration, cure by resting for 24 hours, and collect the inorganic macromolecular polysilicic acid and poly-zirconium chloride flocculant with 5:1 molar ratio of Zirconium/Silicon.

(16) The test results are shown in Table II:

(17) TABLE-US-00002 Turbidity of Precipitated Dosage (In precipitated water DOC Reagent zirconium, mM) water (NTU) (mg/L) Zirconium 0.5 2.7 1.9 tetrachloride Polymerizing 0.5 0.9 0.5 silicate and zirconium chloride

(18) Compared to using zirconium tetrachloride alone, the inorganic macromolecular polysilicic acid and poly-zirconium chloride flocculant with 5:1 molar ratio of Zirconium/Silicon exhibited significantly higher removal rate for turbidity and organics, when the raw water is at <5° C. The method disclosed in this application is proven to be effective in the treatment of low temperature raw water.