REDUCTION OF

HEXAVALENT CHROMIUM

AT THE END OF THE PRESENTATION,

YOU WILL BE ABLE TO UNDERSTAND :

•WHAT IS CHROMIUM• HOW HEXAVALENT CHROMIUM IS FORMED•WHERE THIS SUBSTANCE CAN BE FOUND•WHY HEXAVALENT CHROMIUM IS DANGEROUS• HOW TO REDUCE THE HEXAVALENT CHROMIUM

INTRODUCTION TO CHROMIUM

TRIVALENT FORM

HEXAVALENT FORM

• ESSENTIAL NUTRIENT FOR HUMANS• NON-TOXIC

• Atomic number 24• A hard silver metal used in stainless steel and other alloys

- FOUND IN STEEL, CHEMICAL, LEATHER AND TEXTILE MANUFACTURING- WATER AND SOIL POLLUTION- DANGER TO HUMAN HEALTH• ALTER GENETIC MATERIAL• CARCINOGENIC• ORGAN DAMAGE• FATAL

WHERE HEXAVALENT CHROMIUM / Cr (IV) CAN BE FOUND?

WELDING FUMES

METAL COATING & PROTECTIVE PAINT

DYES AND PIGMENTS

Methods to detect Cr (III) and Cr(VI)

ATOMIC ABSORPTION (AA)

SPECTOMETRY

ION EXCHANGE CHROMATOGRAPHY

HEALTH EFFECTSINGESTION HAZARDS- Erosive to stomach

EYES- Permanent eye damage when direct contact with chromic

acid or chromate dusts

RESPIRATORY TRACT- Hexavalent chromium can irritate nose, throat and lungs

- Ulcers in nasal

SKIN- Dermatitis and skin ulcers

- Worker that sensitive to chromium will cause serious skin rash even in small amount

CANCER and FATAL

HEXAVALENT CHROMIUM WASTE TREATMENT

There are 2-stages of treatment:• STAGE 1 – Reduce Chromium (VI) to Chromium (III)• STAGE 2 - Neutralization

FIRST STAGE

Reduce chromium (VI) to chromium (III)

Using reducing agents:• Sulfur dioxide,• Sodium bisulphate,• Or sodium-meta-bisulfite

Acid : Sulphuric acid

SECOND STAGE(Neutralization)

• Adding Calcium hydroxide (lime) to the wastewater

• Increase and maintain pH of 8.0 or higher

• For the precipitation of chromium hydroxide to occur.

Then, the precipitate can be easily separated (flocculation, coagulation and sedimentation) and then dispose

Collected as sludge

Main disadvantages of this treatment method are:

• Need to reduce wastewater pH between 2 and 3 to assure rapid and complete reduction.

• The acidic wastewater need to be neutralized before discharge.

• These steps consume large amount of chemicals and tend to increase the volume of sludge with unreacted precipitants.

END OF TOPIC