Manufacturing of 10 TPD of Sodium Dichromate from

Chrome Ore

Aatica Aumbreen, Sana Tayyab, Madiha Naz, Najma Sulttana & Ayesha Shahid

NFC Institute of Engineering & Fertilizer Research, Faisalabad

Abstract

This report deals with the design calculations of Sodium Dichromate from Chrome Ore production along with their

relevant aspects such as material and energy Balances, Instrumentation and Process Control, HazOp study and Cost

Estimation.

Introduction

The raw material for the manufacturing of

sodium dichromate and other chromium

compound is chrome ore, so called cromite, a

chromium iron oxide containing

approximately 50% Cr2O3, the balance being

principally FeO, Al2O3, SiO2, & MgO.

Throughout the 20th Century, the use of

Chromium (Cr) has been associated with

providing pigments for textiles and paint,

protecting stainless steel and non-ferrous

alloys, enhancing leather processing and

timber preservation, creating catalysts for

chemicals, and preserving surface treatments.

Art deco designs in the 1930s and chrome-

plated automobiles in the 1960s were

trademarks of their eras. More recently,

chromium (particularly hexavalent

chromium, (Cr+6) has been associated

hazards to human health and the

environment.

In 2001, the United States consumed an

estimated 14% of the world chromite ore

production in the form of imported materials:

chromite ore, chemicals, ferroalloys, and

metal. Consumption of Chromium

ferroalloys and metal was predominantly for

the production of stainless steal and heat-

resistant steel and super alloys. The value of

chromium material consumption was

estimated to be approximately $327 million

in 2001.

Chromium is consumed in metallurgy,

chemical, and refractory industries. In the

United States, an estimated 87% of

chromium is consumed by metallurgy

industries, 10% by chemical industries, and

3% by refractory industries. Chromite ore is

mined and converted to ferrochromium,

chromium chemicals, and incorporated into

chromite-containing refractories.

Methodology

Manufacture of Sodium chromate from

Chrome Ore

1. Grinding(Size reduction)

2. Mixing with limestone and soda ash

3. Roasting(Single stage)/(Two stage)

4. Crushing of product

5. Leaching

Manufacture of Sodium dichromate from

Sodium chromate

1. The sulfuric acid conversion process

is carried out in an agitated reactor. The

discontinuous and continuous addition of

sulfuric acid to sodium chromate solution up

to pH of 3 is technically simple. The sodium

sulfate solubility is low in sodium dichromate

solutions, this producing sodium sulfate

crystals during the reaction.

2. The resulting solution sodium

dichromate dihydrate is then evaporated to

70% by weight.The sodium sulfate has

inverse solubility which permits the removal

of the remaining sodium sulfate (impurity in

bichromate) by heating and evaporating the

solution. The sodium sulfate is separated,

washed, and dried to a salable product for use

in the paper industry.

3. The resulting hot solution from the

evaporation is cooled to produce the sodium

bichromate crystals. The crystallization can

be carried out batch wise in agitated tanks or

continuously in flash cooling or surface

cooling crystallizers.

4. The sodium bichromate is

crystallized as a dihydrate crystal which is

separated and washed in a centrifuge. The

Na2Cr2O7 • 2H2O crystals are dried.

5. The resulting mother liquor can be

sold as a low-purity solution or used for

processing to produce other chrome

chemicals, or recycled to the evaporators to

produce additional bichromate.

Mechanical Design, Material and Energy

Balances were applied across following

units:

1. Rotary Kiln

2. Reactor

3. Evaporator

4. Condenser

5. Crystallizer

6. Rotary Dryer

7. Lifters for Rotary Dryers

Conclusion

Sodium dichromate is also used in the

manufacture of photographic films, flavors,

essential oils, saccharin, pharmaceuticals,

pyrotechnics explosives, safety matches,

chrome glues and adhesives, wood stains,

poison fly paper, process engraving and

lithography, synthetic perfumes, chrome

alum manufacture, alloys, ceramic products

and many other chemicals and is excessively

available in Pakistan. With the help of this

design report and experienced engineers, a

successful plant can be erected that could

enable us to use out own chromite ore

reserves.

References

1. PETER and TIMMERHAUS , ‘’ Plant

Design and Economics for Chemical

Engineers, ‘’ 2003.

2. PERRY , ‘’ Chemical Engineers Hand

Book’’, 1997.