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70 REMOVAL OF CHROMATE FROM SALT CAKE Wei-chi Ying, Scientist Robert L. Zeller III, Senior Research Scientist Russell Morgan, Manager Occidental Chemical Corporation Grand Island, New York 14072 Dianliang Xu, Associate Professor Shanghai Jiao Tong University People's Republic of China INTRODUCTION Occidental Chemical Corporation operates the largest facility for production of chromium chemicals in the Western hemisphere and is one of the largest producers in the world. The plant is located at Castle Hayne, North Carolina and produces chromic acid, sodium bichromate, and sodium sulfate (salt cake). The Castle Hayne plant became operational in 1971 and represented a significant technological advancement in chromium chemicals manufacture (Figure 1) and is still at the leading edge of that technology. Chromite ore, sodium carbonate, and a small amount of lime, are blended and roasted in a kiln at temperatures exceeding 1200°C to oxidize the Cr(III) in the ore to Cr(VL). The kiln end Product is quenched and leached to form raw sodium chromate liquor. The raw liquor contains soluble iron, aluminum, and other components from the ore, and is purified through a number of pH adjustment and filtration steps. The purified sodium chromate liquor is reacted with recycled sodium bisulfate to form sodium bichromate and salt cake. Evaporation of the sodium bichromate results in the precipitation of salt cake crystals, which are washed, dried, and packaged. The salt cake crystals are used primarily by paper manufacturers in the kraft pulping process. The concentrated bichromate liquor produced can be sold as product or processed further to generated sodium dichromate crystals. However, the majority of the concentrated sodium bichromate solution is reacted with sulfuric acid to form chromic acid crystals and sodium bisulfate. The chromic acid crystals are separated by filtration, melted, and then flaked to produce a purified product. The filtrate from this process, primarily comprised of sodium bisulfate, is recycled for reaction with sodium chromate. Salt cake typically contains 500 to 700 ppm Cr(VI) as Na2Cr04 Chromate removal is essential for increasing the marketability and value of this product. A variety of chromate removal technologies, including reduction/precipitation and separation of chromate, have been investigated. This paper Filtrate (NaHSO,) Ore J- Sodium Chromate H2SO, Sodium Bichromate Salt Cake Chromic Acid Cr Removal Purified Salt Cake Solution Figure 1. Process flow diagram for production of chromium chemicals. 47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118 Printed in U.S.A. 651
Object Description
Purdue Identification Number | ETRIWC199270 |
Title | Removal of chromate from salt cake |
Author |
Ying, Wei-Chi Zeller, Robert L. Morgan, Russell Xu, Dianliang |
Date of Original | 1992 |
Conference Title | Proceedings of the 47th Industrial Waste Conference |
Conference Front Matter (copy and paste) | http://e-archives.lib.purdue.edu/u?/engext,43678 |
Extent of Original | p. 651-668 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital object copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Date Digitized | 2009-12-10 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Resolution | 300 ppi |
Color Depth | 8 bit |
Description
Title | page 651 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Transcript | 70 REMOVAL OF CHROMATE FROM SALT CAKE Wei-chi Ying, Scientist Robert L. Zeller III, Senior Research Scientist Russell Morgan, Manager Occidental Chemical Corporation Grand Island, New York 14072 Dianliang Xu, Associate Professor Shanghai Jiao Tong University People's Republic of China INTRODUCTION Occidental Chemical Corporation operates the largest facility for production of chromium chemicals in the Western hemisphere and is one of the largest producers in the world. The plant is located at Castle Hayne, North Carolina and produces chromic acid, sodium bichromate, and sodium sulfate (salt cake). The Castle Hayne plant became operational in 1971 and represented a significant technological advancement in chromium chemicals manufacture (Figure 1) and is still at the leading edge of that technology. Chromite ore, sodium carbonate, and a small amount of lime, are blended and roasted in a kiln at temperatures exceeding 1200°C to oxidize the Cr(III) in the ore to Cr(VL). The kiln end Product is quenched and leached to form raw sodium chromate liquor. The raw liquor contains soluble iron, aluminum, and other components from the ore, and is purified through a number of pH adjustment and filtration steps. The purified sodium chromate liquor is reacted with recycled sodium bisulfate to form sodium bichromate and salt cake. Evaporation of the sodium bichromate results in the precipitation of salt cake crystals, which are washed, dried, and packaged. The salt cake crystals are used primarily by paper manufacturers in the kraft pulping process. The concentrated bichromate liquor produced can be sold as product or processed further to generated sodium dichromate crystals. However, the majority of the concentrated sodium bichromate solution is reacted with sulfuric acid to form chromic acid crystals and sodium bisulfate. The chromic acid crystals are separated by filtration, melted, and then flaked to produce a purified product. The filtrate from this process, primarily comprised of sodium bisulfate, is recycled for reaction with sodium chromate. Salt cake typically contains 500 to 700 ppm Cr(VI) as Na2Cr04 Chromate removal is essential for increasing the marketability and value of this product. A variety of chromate removal technologies, including reduction/precipitation and separation of chromate, have been investigated. This paper Filtrate (NaHSO,) Ore J- Sodium Chromate H2SO, Sodium Bichromate Salt Cake Chromic Acid Cr Removal Purified Salt Cake Solution Figure 1. Process flow diagram for production of chromium chemicals. 47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118 Printed in U.S.A. 651 |
Resolution | 300 ppi |
Color Depth | 8 bit |
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