Title of Invention

A PROCESS FOR THE RECOVERY OF NICKEL AND CHROMIUM FROM THE PICKLING BATH SLUDGE OF STAINLESS STEEL.

Abstract This invention relates to a process for the recovery of nickel and chromium from the pickling bath sludge of stainless steel. The process comprises treating leach liquor containing sodium chromate and its acidification with HCL,reducing the same with sodium sulphite and then hydrolysing with NH4OH to precipitate chromium as Cr(OH)3which on calcinations yields chromium oxide (CrO3) .From the chromium free sludge, nickel was recovered as ferro-alloys by carbothermic industries .The quantitative recoveries of nickel and chromium is in the range of about 93-95% and 95-96% respectively.
Full Text This invention relates to a process for the recovery of nickel and chromium from he pickling bath sludge of stainless steel. This invention particularly relates to a process for the recovery of nickel and chromium from the sludge generated during the pickling of the stainless steel. This invention will be useful for the stainless steel and ferroalloys producing industries.
Background of the Invention
In stainless steel industry, hot rolled stainless steel coils are pickled prior to cold rolling using mixtures of nitric acid and hydrofluoric acid to completely remove the oxide scales from the surface of the stainless steel. During this pickling process, a portion of the nickel and chromium enter into the pickling solution. The waste mixed acid is then neutralised with lime before discharging it to the drain. This process of neutralising the waste pickled acid generates a sludge, which contains hydroxides of nickel, chromium and iron, along with calcium fluoride and unreacted lime. The amount of nickel and chromium entering into the sludge is substantial and the amount of sludge generated is also quite large. To the best of our knowledge, no published literature or patent is available to address the problem of recovering nickel and chromium from the pickling bath sludge of stainless steel.
The main object of the present invention is to provide a process to recover nickel and chromium from the pickling bath sludge of stainless steel, which obviates the draw backs as detailed above.
Another object of the present invention is to provide a process for the recovery of nickel and chromium in a suitable usable form, from the pickling bath sludge of stainless steel, through a pyro-cum-hydrometallurgical route.
The process of present invention involves in the selective separation of chromium from the sludge and conversion of the chromium free sludge into ferro-nickel. The chromium present in the sludge was converted to water soluble sodium chromate by roasting with sodium carbonate and was selectively leached out with water. The reaction involved in the sodium carbonate roasting of the sludge may be presented as : 4Cr(OH)3 + 4Na2O3 + 3O2 = 4Na2CrO4 + 4CO2 + 6H2O The novelty of the invention lies in treating leach liquor containing sodium chromate and its acidification with HC1, reduced with sodium sulphite and then hydrolysed with NH4OH to precipitate chromium as Cr (OH)3 , which on calcination has yielded chromium oxide ( Cr2O3). From the chromium free sludge, nickel was recovered as ferro-nickel by carbothermic reduction.
Accordingly, the present invention provides a process for the recovery of nickel and chromium from the pickling bath sludge of stainless steel which comprises:
(i) collecting the pickling bath sludge of stainless steel,
(ii) mixing the sludge with sodium carbonate and roasting in the temperature range of 600-1000°C,
(iii) leaching of the said roasted sludge with water at ambient temperature for 2-6 hrs and separating the solids and liquid by filtration,
(iv) heating the sodium chromate solution obtained in step (iii) to a temperature of 60-70°C, acidifying with HC1 , reducing the chromium with sodium sulphite and then hydrolysing by the addition of NH4OH and precipitating the chromium as Cr(OH)3,
(v) separating the solids and liquid by filtration,
(vi) calcining the (Cr(OH)3 precipitate obtained in step (v) to obtain chromium oxide (Cr2O3),
(vii) mixing the chromium free sludge obtained in step (iii) with carbon reductant and pelletizing to a size of 6-9 mm,
(viii) drying the pellets initially in air and later in an oven at temperature of 100-110
°C,
(ix) smelting the dried pellets to get ferro-nickel (Fe-Ni).
In an embodiment of the present invention the pickling bath sludge comprises of about 3.8% Ni(OH)2, about 57.2% Fe(OH)3,about 57.2%Fe(OH)3,aboutl4% Ca(OH)2 and about 18% CaF2.
In another embodiment of the present invention the ratio of the sludge to the leachant varies from 1:3 to l:10(w/v).In another embodiment of the present invention the temperature of roasting the sludge varies in the range of 600-1000°C.
In yet another embodiment of the present invention the amount of sodium carbonate used during the roasting of the sludge is in the range of 5-20% (w/w) of the sludge.
In still another embodiment of the present invention the calcination temperature of the chromium hydroxide is in the range of 450-850°C.
In still another embodiment of the present invention the carbonaceous reductant is selected from coal, coke and petroleum coke.
In still another embodiment of the present invention recovery nickel and chromium from the pickling bath sludge of stainless steel are in the range of about 93-95 and about 95-96%.
The following examples are given by way of illustration and therefore should not be construed to limit the scope of this invention.
EXAMPLE-1
1000 grams of the stainless steel pickling bath sludge containing 3.8% Ni(OH)2) 5.2% (Cr(OH)3, 57.2% Fe(OH)3, 14% Ca(OH)2 and 18% CaF2 was mixed thoroughly with 100 grams of sodium carbonate and roasted at 700°C in a muffle furnace for 2 hrs and then leached with water for 4 hrs. After leaching, the solids and liquids were separated by filtration The leach liquor containing sodium chromate was heated to 60 °C and acidified with HC1 , and the chromium was reduced with sodium sulphite and hydrolysed with ammonia and precipitated as Cr(OH)3. The chromium hydroxide was dried and calcined and chromium oxide (Cr2O3) was obtained.
The chromium free sludge was mixed with 100 grams of powdered coal of 60 mesh BSS size and palletised into 6-9 mm size. These pellets were dried initially in air and later in an oven at 100°C. The oven dried pellets were smelted and ferro-nickel was obtained.
The recoveries of nickel and chromium were 94.4% and 96.2% respectively. The grade of ferro-nickel obtained was 26.3% Ni.
EXAMPLE- 2
1000 grams of the stainless steel pickling bath sludge containing 3.8% Ni(OH)2, 5.2% (Cr(OH)3) 57.2% Fe(OH)3, 14% Ca(OH)2 and 18% CaF2 was mixed thoroughly with 120 grams of sodium carbonate and roasted at 700°C in a muffle furnace for 2 hrs and then leached with water for 4 hrs. After leaching, the solids and liquids were separated by filtration The leach liquor containing sodium chromate was heated to 70°C and acidified with HC1, and the chromium was reduced with sodium sulphite and hydrolysed with ammonia and precipitated as Cr(OH)3. The chromium hydroxide was dried and calcined and chromium oxide ( Cr2O3) was obtained.
The chromium free sludge was mixed with 100 grams of powdered coal of 60 mesh BSS size and palletised into 6-9 mm size. These pellets were dried initially in air and later in an oven at 110°C. The oven dried pellets were smelted and ferro-nickel was obtained.
The recoveries of nickel and chromium were 95.2% and 96.3% respectively. The grade of ferro-nickel obtained was 25.6%Ni.
EXAMPLE-3
1000 grams of the stainless steel pickling bath sludge containing 3.8%Ni (OH)2, 5.2% (Cr(OH)3, 57.2% Fe(OH)3, 14% Ca(OH)2 and 18% CaF2 was mixed thoroughly with 110 grams of sodium carbonate and roasted at 700°C in a muffle furnace for 2 hrs and then leached with water for 4 hrs. After leaching, the solids and liquids were separated by filtration The leach liquor containing sodium chromate was heated to 60 °C, and acidified with HC1 , and the chromium was reduced with sodium sulphite and hydrolysed with ammonia and precipitated as Cr(OH)3. The chromium hydroxide was dried and calcined and chromium oxide (Cr2O3) was obtained.
The chromium free sludge was mixed with 100 grams of powdered coal of 60 mesh BSS size and palletised into 6 mm size. These pellets were first air dried and later in an oven at 100°C. The oven dried pellets were smelted and ferro-nickel was obtained.
The recoveries of nickel and chromium were 93.4% and 95.5% respectively. The grade of ferro-nickel obtained was 25.7% Ni.
Advantages
The main advantages of the present invention are:
1. Quantitative recoveries of nickel (94% ) and chromium (96%) from the
pickling bath sludge stainless steel.
2. The process can also be used for the recovery of nickel and Chromium from the
mill scale of the stainless steel.









We claim:
1. A process for the recovery of nickel and chromium from the pickling
bath sludge of stainless steel, which comprise :
(i) collecting the pickling bath sludge of stainless steel,
(ii) mixing the sludge with sodium carbonate and roasting in the temperature range of 600-1000°C,
(iii) leaching of the said roasted sludge with water at ambient temperature for 2-6 hrs and separating the solids and liquid by filtration,
(iv) heating the sodium chromate solution obtained in step (iii) to a temperature of 60-70°C, acidifying with HC1 , reducing the chromium with sodium sulphite and then hydrolysing by the addition of NH4OH and precipitating the chromium as Cr(OH)3,
(v) separating the solids and liquid by filtration,
(vi) calcining the (Cr(OH)3 precipitate obtained in step (V) to obtain chromium oxide (Cr2O3),
(vii) mixing the chromium free sludge obtained in step (iii) with carbon reductant and pelletizing to a size of 6-9 mm,
(viii) drying the pellets initially in air and later in an oven at temperature of
100-110°C,
(ix) smelting the dried pellets to get ferro-nickel (Fe-Ni).
2. A process as claimed in claim 1, wherein the pickling bath sludge comprises of 3.8% Ni(OH)2, 5.2% Cr(OH)3, 57.2 %Fe(OH)3, 14%Ca(OH)2 and 18% CaF2.
3. A process as claimed in claim 1, wherein the ratio of the sludge to the leachant varies from 1:3 to 1:10 (w/v)
4. A process as claimed in claim 1, wherein the amount of sodium carbonate used during the roasting of the sludge is in the range of 5-20% (w/w) of the sludge.
5. A process as claimed in claim 1, wherein in step (vi), the calcination temperature of the chromium hydroxide is in the range of 450-850°C.
6. A process as claimed in claim 1, wherein the carbonaceous reductant is selected from coal, coke, petroleum coke.
7. A process for the recovery of nickel and chromium from the pickling bath sludge of stainless steel substantially as herein described with reference to examples.


Documents:

419-DEL-2004-Abstract (22-01-2010).pdf

419-del-2004-abstract.pdf

419-DEL-2004-Claims (22-01-2010).pdf

419-del-2004-claims.pdf

419-DEL-2004-Correspondence-Others (22-01-2010).pdf

419-DEL-2004-Correspondence-Others-(28-08-2006).pdf

419-del-2004-correspondence-po.pdf

419-del-2004-correspondence.pdf

419-DEL-2004-Description (Complete) (22-01-2010).pdf

419-del-2004-description.pdf

419-del-2004-form-18-(28-08-2006).pdf

419-DEL-2004-Form-3 (22-01-2010).pdf

419-del-2004-form1.pdf

419-del-2004-form2.pdf

419-del-2004-form3.pdf

419-del-2004-form5.pdf


Patent Number 241004
Indian Patent Application Number 419/DEL/2004
PG Journal Number 25/2010
Publication Date 18-Jun-2010
Grant Date 14-Jun-2010
Date of Filing 11-Mar-2004
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address Rafi Marg, New Delhi 110001.
Inventors:
# Inventor's Name Inventor's Address
1 MADHUKAR GANAPTHRAO BODAS National Metallurgical Laboratory, Jamshedpur 831001, JHARKHAND STATE, INDIA.
2 DAITA SREE RAMACHANDRA MURTHY National Metallurgical Laboratory, Jamshedpur 831001, JHARKHAND STATE, INDIA.
PCT International Classification Number B09B 3/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA