[Share] How To Remove Chromium 6 From Water Effectively ?

Chromium-generated water is during the process of chromium plating, passivation is galvanizing, copper and their alloys. Ion Cr + 6 has an extreme toxicity. There are many types of chromium water treatment methods, mainly chemical method, electrolysis method, ion exchange method, activated carbon adsorption method, evaporation concentrate method, etc. In this article AXIOS REVIEW will find out how to remove chromium 6 from water .

What is Chromium ?

How to remove chromium 6 from water

Chromium is a compound widely used in industrial applications. Most of the chromium in the environment is discharged from the wastewater of these industrial applications.

Chromium also occurs naturally in activities such as volcanic eruptions, weathering of soil and rock geology.

In addition, there are other sources such as fossil fuel burning, chromate production, plastic production, metal electroplating and leather industries.

How to remove chromium 6 from water

Chromium is used in the leather and paper industry, pulp and rubber applications

Health risks related to Chromium 6 – How toxic Chromium 6 is?

How to remove chromium 6 from water

Even a small contact can cause liver and kidney damage, skin ulcers also affect the nervous system.

The safety level of chromium-6 is known to cause cancer in animals and humans in tap water around the country.

The environmental research team (EWG) analyzed data collected by the EPA about the amount of chromium-6 in water. The results showed that, if left untreated, chromium-6 in tap water would cause more than 12,000 new cancer cases.

How to remove chromium 6 from water

Research on chromium-6 has been identified by breathing particles that can cause lung cancer. The US government imposes strict limits on chromium-6 levels in the air in the workplace.

The chemicals have also been shown to damage the liver, reproductive problems and greater risks for infants and children, those taking antacids, and people with poorly functioning liver.

For plants, it can reduce the rate of photosynthesis

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How to remove chromium 6 from water

Chemical method

This method of remove chromium 6 from water is the method of reducing precipitation.

Step 1: In acidic conditions, use S02, NaHS03, FeS04, N2H4H20, and close cast as a reducing agent to reduce Cr + 6 to Cr + 3.

Step 2: For alkaline substances Na2C03, NaOH, CaO … to raise the pH of water, make Cr + 3 into Cr (OH) 3 precipitate, then remove.

How to remove chromium 6 from water

 

How to remove chromium 6 from water

Method of using NaHSo3

This method uses NaHSO3 or Na2C03, Na2S03, Na2S205 in the water to reduce Cr + 6 to Cr + 3. The reaction is as follows:

The reaction produces Cr + 3, after raising the pH = 6.5 – 7.5, forming Cr (OH) 3 precipitates, get the precipitate. The end of the reaction was judged by the colorimetric method, due to the reaction between Cr + 6 and Diphenyl carbazide, forming a red compound. Currently, using NaHSO3 dike to treat Cr + 6, there are two methods: concentrated or flow treatment.

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Method of centralized treatment is: to discharge chromium-containing water into tanks, when it reaches a certain amount, pump it into a reactor, conduct a reduction-precipitation treatment. The technology is as follows:

How to remove chromium 6 from water
  • Water tanks reach a certain volume, stir, use H2S04 to adjust pH.
  • Analysis of Cr + 6 content;
  • Based on the concentration of Cr + 6 calculated for proportional reducing agent, stirring by compressed air, time of 15 minutes;
  • Leave to stand for many hours, after analyzing the content of Cr + 6, can it meet the treatment requirements?
How to remove chromium 6 from water
  • When Cr + 6 reaches the set standard. Pump melon into the precipitation tank, stir well, and add 20% NaOH, adjust pH = 6.5 – 7. Stir for 5 minutes:
  • Stand still for many hours, slicing water above or using water again;
  • Retrieving precipitation, recovering treatment.
  • The characteristics of this method are: It is possible to handle many types of chromium-containing water, bringing many kinds of chromium-containing sewage into the tank, intermittent treatment, to adjust pH, easy for chemicals , control response.
  • The treatment method on the flow is the method of thoroughly treating the water. It has the following characteristics: fewer chemicals added, high practicality, high effectiveness, suitable for a small area, and less investment. Cr (OH) 3 precipitate. Wash 2-3 times. SO4-2 original cleaning base, concentrated, dried, heated 1200 ° c, can be used with Cr2O3.

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Method of using FeS04 – lime water

Method of using FeSO4 – lime water is the oldest method of pouring and treating chromium, suitable for cutting chromium water with a large change in concentration. 

Adjust chromium water with pH = 3, water in the form of Cr2O4-2, give FeSO4, Fe + 2 reducing Cr + 6 to Cr + 3 then add lime water, adjust pH = 7 – 9, Cr + 3 and Fe + 3 will form precipitated hydroxide compound.

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Method of adsorption of activated carbon

Activated carbon can adsorb Cr + 6, also reducing effect. Therefore, activated carbon is both an adsorbent and a chemical to clean out chromium. In an acid environment, pH <3, activated carbon adsorbs Cr + 6 in the surface tank, reducing to Cr + 3 When activated carbon is adsorbed to saturation, put into the acid solution, Cr + 6 ion will be adsorbed. Activated carbon adsorption equipment is made into sets, and is marketed.

How to remove chromium 6 from water

How to remove chromium 6 from water

Regenerating activated carbon using two methods: alkali regeneration 

and acid regeneration. Renewing and checking NaOH solution 8 – 15%. The amount of regenerated substance and the volume of activated carbon are the same; the exposure time is 30-60 minutes. Activated carbon after alkaline regeneration, proceed activated by acid.

Concentration H2S04 5 – 10%, the amount used is half the activated carbon. Acid regeneration solution is H2S04 10 – 20%, using half the activated carbon, soaking time 4-6 hours. Chromate regeneration solution, can be used to make polish. In production, the technology used for adsorption of activated carbon is two or three columns.

Ion exchange method

Ion exchange method is the method of using high molecular resins to conduction exchange. In the resin with the active root group, the ability to exchange ions, insoluble in water, acids, alkalis, and organic substances, exchange or adsorb some ionic substances, then use which chemicals that plastic, makes the adsorbent escape.

How to remove chromium 6 from water

The selective exchange effect of ion exchange resins can remove harmful impurities such as chromium, copper, nickel, cyanide … This method is used to treat low-concentration water, large volumes of water, possibly recover metals and rewash water.

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The process of water treatment of the ion exchange method is as follows:

Waste water filtration + Positive ion exchange -> Negative ion exchange -> Regeneration of plastic -> Concentration of chrome recovery.

a. Water filter

How to remove chromium 6 from water

Water before going into the positive ion exchange column needs to be filtered to eliminate the mechanical impurities, suspensions, avoid plastic dirt by sand filtration method, or plastic filter with many policlovinyl (PVC) holes.

b. Positive ion exchange resins

To improve the cleanliness of chromic acid, remove other metal ions, it is necessary to conduct a positive ion exchange. Usually, use strong acid resin with the model number 732, effluent discharge, high H + concentration, reduced pH, Cr + 6 in water exists in the form of Cr2O7-2.

c. Negative ion exchange resins

After the water has exchanged positive ion column, going into the negative ion column, the resin will adsorb Cr2O7-2 and Cr2O7-2 in the water, OH-1 in the plastic transferred into the solution. It is common to use weak alkaline ion resins 710.

d. Plastic recycling

Choose the right chemical, make the adsorbent on the plastic released, and make the plastic recover the adsorption capacity.

How to remove chromium 6 from water

Negative ion regeneration: Commonly used regenerative substances are: Cr2O7-2 exchanges NaOH, OH-1 radical in NaOH, and Cr2O4-2 adsorbed in plastic. Regenerating substances often use NaOH solutions 4 – 10%.

Regeneration of positive ionic resins: Use H-1 ions in acid to replace metal adsorbed ions adsorbed in resins, converting them to H type resins.

Commonly used regenerants are H2S04 3 – 5% or HCl 1 – 3 mol / 1. The amount of recycled substance is 3 times the plastic volume.

e. Acid recovery

The Na2Cr2O7 or Na2CrO4 solution obtained at regeneration can be reduced with a strong acid-ion resin 732. Because of the initial reduction of Na at a low pH, Cr + 6 in water exists as colored Cr2O7-2 orange-red. As the Na reduction nears the endpoint, the pH increases, the leading solution is CrO3 yellow. After Na reduction, low CrO3 concentration, and Cl + 1 ion, need to concentrate and remove chlorine to use

Method of water treatment by ion-exchange method

In the production of the water treatment process by ion exchange method, the positive ion exchange column type H, the two negative ion columns of type OH, and the positive ion type of sodium ion are formed.

To conclude, chromium 6 is toxic in various ways, so it is essential for everyone to acknowledge its possible effects on human bodies and find the solution to thoroughly remove chromium 6 from water.

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