CN104478129B - A kind of method removing Trace Cadmium in the aqueous solution - Google Patents

Abstract

The present invention relates to wastewater processing technology, particularly a kind of method removing Trace Cadmium in the aqueous solution.The present invention includes following steps: A, adjust pH, B, precipitin reaction, C, coagulation, D, water outlet adjust pH, the present invention utilizes acid base indicator thymolphthalein indicator and phenolphthalein indicator effectively to control the pH value be suitable for cleverly, avoid and use pH test paper to have the systematic error that has of colour developing error or pH meter can not obtain accurate pH value, make a large amount of cadmiums can form cadmium hydroxide precipitation, the add-on of control alkali that again can be suitable, guarantee after adding carbonate remaining cadmium form cadmium carbonate particle as far as possible, cadmium Cd≤0.0032mg/L in solution, ferron good coagulation is utilized to be removed by the throw out coagulating sedimentation of cadmium, and sedimentation centrifugal removing make solution incarnadine become colourless containing acid adding in cadmium throw out solution after coagulation, pH < 8.0 can discharge.

Description

A method for removing trace cadmium in aqueous solution

technical field

The invention relates to waste water treatment technology, in particular to a method for removing trace cadmium in aqueous solution.

Background technique

Cadmium pollution in water has attracted worldwide attention. With the increasing frequency of water body cadmium pollution outbreaks and increasingly serious pollution, local departments in key river basins and water-environmentally sensitive areas implement the Class II standard (Cd ≤0.005mg/L), in 2006, my country's newly promulgated "Drinking Water Hygienic Standards" also strictly limited the concentration of cadmium, limiting Cd≤0.005mg/L. There are many treatment methods for cadmium-containing wastewater, and the treatment methods adopted are different according to the cadmium content and cadmium existence form. At present, cadmium removal methods mainly include physical methods, chemical methods, physical chemical methods and biological methods, among which chemical methods are mainly used, including chemical adsorption method, chemical precipitation method (hydroxide precipitation method and sulfide precipitation method), electrodeposition method, etc. Chemical redox method, iron oxidation method, coagulation precipitation method, chelation precipitation method, foam separation method, etc.

The patent "a method for removing trace amounts of cadmium in aqueous solution" (authorized announcement number CN102249450B) is characterized by cultivating and dissecting plants grown in a chromium environment, controlling the pH value of the solution, and adding iron-containing reagents and carbonates And phosphate or molybdate, etc., basically remove cadmium in cadmium-containing waste liquid. The raw materials used in this invention are economical and easy to obtain, no harmful elements are added to the system, the waste water treatment time is short, the amount of reagents is less, and the amount of waste residue is less. The cadmium content in the treated aqueous solution is less than 0.01mg/L, which can be discharged into secondary level pipe network. Although it is an environmentally friendly treatment method, it can be widely used in the treatment of cadmium-containing wastewater discharged from metal processing industry, electroplating industry, leather industry and textile industry. However, this method cannot meet the requirements of local departments in key river basins and water environment-sensitive areas to implement the "Surface Water Environmental Quality Standards" (GB3838-2002) Class II standards or the "Drinking Water Hygienic Standards" (GB5749- 2006 ) (Cd≤0.005mg/L) requirements.

Contents of the invention

The purpose of the present invention is to provide a method for removing trace amounts of cadmium in aqueous solution, which can meet the requirements of the cadmium discharge limit of production enterprises by local departments in key river basins and water environment sensitive areas to implement Class II of the "Surface Water Environmental Quality Standard" (GB3838-2002) Standards or "Drinking Water Hygienic Standards" (GB5749-2006) (Cd≤0.005mg/L) requirements.

Technical solution of the present invention: a method for removing trace amounts of cadmium in an aqueous solution, comprising the following steps:

A. Adjust the pH value: first drop 3-10 drops of thymolphthalein 90% ethanol solution indicator with a mass concentration of 1‰ in the aqueous solution to be treated containing divalent cadmium, and then use alkali (sodium hydroxide or calcium hydroxide) Adjust the solution so that the solution turns from colorless to blue, and the pH of the solution is ≥ 9.4;

B. Precipitation reaction: add precipitant carbonate (sodium carbonate or sodium bicarbonate) 5-50 mg/L to the aqueous solution to be treated containing divalent cadmium adjusted to pH ≥ 9.4, stirring speed 600r/min, time 1- 10min to react;

C. Coagulation: After the precipitation reaction, add the coagulant iron reagent (ferric chloride or polyferric sulfate) while the stirring speed is adjusted to 200r/min, and the solution changes from blue to colorless, that is, pH<9.4. Add 3-10 drops of phenolphthalein 90% ethanol solution indicator with a mass concentration of 5‰ in the solution, and the solution is bright red. While continuing to stir, add coagulant iron reagent to make the solution change from bright red to light red, that is, control pH ≥ 8 , stirring at a medium speed of 120r/min for 4.5min, stirring at a slow speed of 30r/min for 10min, standing for 20 minutes, settling and centrifuging to remove the cadmium-containing precipitate;

D. Adjust the pH value of the effluent: After coagulation, settle and centrifuge to remove the cadmium-containing precipitate. Add acid (sulfuric acid or hydrochloric acid) to the solution to turn the solution from light red to colorless, and discharge when the pH is less than 8.0.

The present invention uses acid-base indicator thymolphthalein indicator and phenolphthalein indicator, through the research of the hydroxide property of cadmium, the carbonate property of cadmium and the hydrolysis property of ferric chloride, utilizes thymolphthalein indicator to form colorless It turns blue, and the change is obvious and easy to observe. The color change range of thymolphthalein is pH 9.4-10.6, which can well indicate the true value of the solution pH, that is, pH ≥ 9.4, which is conducive to the cadmium in the solution to form cadmium hydroxide precipitation; continue to add 5—50mg/L carbonate makes the remaining cadmium form cadmium carbonate particles; then add iron reagent, use the good coagulation effect of iron reagent to remove the cadmium precipitate, but the pH value drops due to the hydrolysis of iron reagent At the same time, the equilibrium concentration of cadmium dissolution and precipitation is related to the pH value (when pH=7.8, Cd=0.0051mg/L; when pH≥8.0, Cd≤0.0032mg/L.), so the coagulation process adopts precipitation reaction and then stirs the speed. Add the coagulant iron reagent at the same time at 200r/min, the solution turns from blue to colorless, that is, pH<9.4, at this time, add the phenolphthalein indicator dropwise in the solution and the solution turns bright red, continue stirring while adding the coagulant iron reagent Make the solution change from bright red to light red, that is, control the pH ≥ 8, settle and centrifuge to remove the cadmium-containing precipitate solution after coagulation, and basically completely remove the trace cadmium (Cd≤0.0032mg/L) in the cadmium-containing solution; effluent The pH value can be adjusted after coagulation, sedimentation and centrifugation to remove cadmium-containing precipitates. Add acid to the solution to make the solution light red and colorless, that is, pH<8.0 can be discharged.

The advantage of the present invention is that the acid-base indicator thymolphthalein indicator and phenolphthalein indicator are cleverly used to effectively control the appropriate pH value, avoiding the use of pH test paper with color development errors or systematic errors of the pH meter that cannot obtain accurate pH values , so that a large amount of cadmium can not only form cadmium hydroxide precipitation, but also properly control the amount of alkali added to ensure that the remaining cadmium after adding carbonate can form cadmium carbonate particles as much as possible, and the cadmium in the solution Cd≤0.0032mg/L, Use the good coagulation effect of iron reagent to remove the cadmium precipitate by coagulation and precipitation, and after coagulation, settle and centrifuge to remove the cadmium-containing precipitate. Add acid to the solution to make the solution light red to colorless, pH<8.0 can be discharged.

Compared with the patent "a method for removing trace cadmium in aqueous solution" (authorized announcement number CN102249450B), the present invention has the same advantages as the raw materials used are economical and easy to obtain, no harmful elements are added to the system, and the waste water treatment time is short. The operation mode and the range of pH value are controlled, so that the amount of reagents is reduced, the amount of reagents is reduced, the amount of waste residue is reduced, the operation is simple and the cost is low, and there is no need to increase ion exchange or membrane separation equipment after coagulation. The cadmium content is smaller (Cd≤0.0032mg/L), which meets the cadmium discharge limit of production enterprises in key river basins and water environment-sensitive areas. Sanitary Standards for Drinking Water (GB5749-2006) (Cd≤0.005mg/L) requirements. The invention is an environment-friendly treatment method, which can be widely used in the treatment of cadmium-containing waste water discharged from fields such as ore dressing, metallurgy, metal processing industry, electroplating industry, tanning industry and textile industry.

detailed description

Embodiment 1: measure cadmium content and be the aqueous solution 1L of 50mg/L, add 3 drops of Thymolphthalein 90% ethanol solution indicator of mass concentration 1‰ in aqueous solution, adjust solution with calcium hydroxide mass concentration 10% solution then, The solution can change from colorless to blue. The pH value of the solution is pH ≥ 9.4. Add 5mg of sodium carbonate and stir at a speed of 600r/min. After the reaction takes 1min, add the coagulant ferric chloride while stirring at a speed of 200r/min. Make the solution change from blue to colorless, that is, pH<9.4, add 10 drops of phenolphthalein 90% ethanol solution indicator with a mass concentration of 5‰ in the solution, and add the coagulant ferric chloride while continuing to stir to make the solution change from bright red Turn into light red, that is, control the pH ≥ 8, stir at a medium speed of 120r/min for 4.5min, stir at a low speed of 30r/min for 10min, let stand for 20 minutes, settle and centrifuge to remove the cadmium-containing precipitate; add to the solution for removing the cadmium-containing precipitate Sulfuric acid turns the solution from light red to colorless, that is, the pH value is <8, and the concentration of cadmium in the effluent is 0.0031mg/L, which meets the Class II standard of "Environmental Quality Standards for Surface Water" (GB3838-2002) or "Hygienic Standards for Drinking Water" ( GB5749-2006) (Cd≤0.005mg/L) requirements.

Embodiment 2: Measure cadmium content and be 1L of aqueous solution of 50mg/L, drip 6 drops of Thymolphthalein 90% ethanol solution indicator of mass concentration 1‰ in aqueous solution, then adjust solution with sodium hydroxide solution, solution is by colorless Just turn blue, the pH value of the solution is pH ≥ 9.4, add 50 mg of sodium carbonate and stir at a speed of 600r/min, and react for 10 minutes, then add the coagulant ferric chloride solution while stirring at a speed of 200r/min. Change to colorless, that is, pH<9.4, add 6 drops of phenolphthalein 90% ethanol solution indicator with a mass concentration of 5‰ in the solution, and add coagulant ferric chloride while continuing to stir to make the solution change from bright red to light red. That is, control the pH ≥ 8, stir at a medium speed of 120r/min for 4.5min, stir at a low speed of 30r/min for 10min, let stand for 20 minutes, settle and centrifuge to remove the cadmium-containing precipitate. Add hydrochloric acid to the solution for removing cadmium-containing precipitates to turn the solution from light red to colorless, that is, the pH value is <8, and the cadmium concentration in the effluent is 0.0029mg/L, which meets the Class II standard of "Surface Water Environmental Quality Standards" (GB3838-2002) Or the requirements of "Hygienic Standards for Drinking Water" (GB5749-2006) (Cd≤0.005mg/L).

Embodiment 3: measure cadmium content and be the aqueous solution 1L of 50mg/L, add dropwise 10 drops of phenolphthalein 90% ethanol solution indicator of mass concentration 5‰ in aqueous solution, then adjust solution with sodium hydroxide solution, solution changes from colorless to Blue is enough, the pH value of the solution is pH ≥ 9.4, add 25 mg of sodium bicarbonate and stir at a speed of 600r/min, and react for 5 minutes, then add a coagulant polymerized ferric sulfate solution to change from blue while stirring at a speed of 200r/min become colorless, that is, pH<9.4, add 3 drops of phenolphthalein 90% ethanol solution indicator with a mass concentration of 5‰ in the solution, and add coagulant polyferric sulfate while continuing to stir to make the solution change from bright red to light red. That is, control the pH ≥ 8, stir at a medium speed of 120r/min for 4.5min, stir at a low speed of 30r/min for 10min, let stand for 20 minutes, settle and centrifuge to remove the cadmium-containing precipitate. Add hydrochloric acid to the solution to remove cadmium-containing precipitates to turn the solution from light red to colorless, that is, the pH value is <8, and the cadmium concentration in the effluent is 0.0028mg/L, which meets the Class II standard of "Surface Water Environmental Quality Standards" (GB3838-2002) or "Drinking Water Hygienic Standard" (GB5749-2006) (Cd≤0.005mg/L) requirements.

Claims (1)

1. remove the method for Trace Cadmium in the aqueous solution for one kind, it is characterized in that: measure the aqueous solution 1L that cadmium content is 50mg/L, the thymolphthalein 90% ethanolic soln indicator 3 of mass concentration 1 ‰ is dripped at the aqueous solution, then be 10% aqua calcis regulator solution by mass concentration, solution is transformed into blueness by colourless, solution ph and pH >=9.4, add 5mg sodium carbonate, mixing speed 600r/min, after time 1min reacts, adding coagulating agent iron(ic) chloride while stirring speed governing 200r/min, that solution is transformed into by blueness is colourless, i.e. pH < 9.4, drip the phenolphthalein 90% ethanolic soln indicator 10 of mass concentration 5 ‰ in the solution, adding coagulating agent iron(ic) chloride while continuing to stir makes solution become incarnadine by bright red, i.e. control pH >=8, middling speed 120r/min stirs 4.5min, low speed 30r/min stirs 10min, leave standstill 20 minutes, sedimentation centrifugal removing are containing cadmium throw out, solution is made to become colourless by incarnadine in removing containing adding sulfuric acid in cadmium throw out solution, i.e. pH value < 8, water outlet cadmium concentration is 0.0031mg/L, reaches the requirement of GB3838-2002 " water environment quality standard " II class standard or GB5749-2006 " drinking water sanitary standard " Cd≤0.005mg/L.