Title of Invention

"A PROCESS FOR THE PREPARATION OF ELECTRONIC GRADE STRONTIUM CARBONATE

Abstract An improved process for preparation of electronic grade strontium carbonate comprising of powdered celestite one as hearein described, industrial coke, such as coal is powdered form, subjecting the reaction mixture to reduction preferably in a vertically mounted tubular reactor at a temperature of 400-950°C for a period of 1-2 hours in a oxygen free atmosphere to obtain water soluble SrS, said SrS was dissolved as herein described, and carbonazing said SrS to obtain electronic grade strontium carbonate.
Full Text FIELD OF THE INVENTION
This invention relates to a process for the preparation of electronics grade strontium carbonate.
Celestite ore is a unique starting material for the manufacture of variety of Sr-chemicals, such as SrCO3, SrCl 1, sr(NO3)2, Sr(OH)2, SrO, etc. In this, so called 'black-ash process' the reduction of celestite is carried out in rotary kiln at high temperature of the order of 400-950°C in the presence of carbon/coke as a reducing agent.
In the course of reduction prime reducing agent is carbon monoxide, which intern is generated in-situ by the reduction of carbon dioxide by carbon. The reactivity of coal is generally co-related by its reactivity with C02 to generate CO.
Earlier study of kinetics of reduction of celestite by carbon is very limited. Few scientists have carried out mechanistic studies of the reduction of SrS04 by carbon. All are univerious of the opinion that the initial reduction of celestite with carbon takes place according to


SrSO4 + 4C → SrS + 4CO (1)
Where both celestite and carbon are in contact. The CO generated dilluses and reacts with celestite, which is not in contact with carbon, according to :
SrS04 +4CO → SrS + 4CO2 (2)
The C02 diffuses back into carbon to generate more CO according to Baudard reaction :
C02 + C → 2CO (3)
Thus, in the solid state reaction of celestite, CO is gasco.is intermediate. Many workers ( Nadiradze et al. 1978, Pedak et al. 1969, Pedak et al. 1972 ) have studied the reduction of celestite, using reducing agent like H2 and mixture of 112 & CO at high temperature. This reduction suffers from two main disadvantages:
1. Large excess of gaseous reductant is required.
2 The nature of solid and gaseous product varies depending upon the composition of reducing gases & reaction conditions. Considering the above disadvantages, safety aspects, the process is lacking in economical viability. Carbothermic reduction of celestite has the advantage of giving definite specified product depending on the reaction temperature i.e. SrS as a unique product.
Gitis et al (1985) and Lepsin et al (1988), have studied the reduction using stoichiometric amount of carbon and through intermediate temperature in the range of 600-700°C at loading zone and 1200-1300°C at discharging zone of rotary kiln. Due to the high discharging zone temperature the process has following disadvantages.
1) High electric energy requirement
2) Sintering of the reactants & products
3) Difficulties in the selection of material of construction for the reactor system for
commercial plant.
CARBONATE PRECIPITATION:
As such not much literature is available on electronic grade strontium carbonate Limited information is available in the Kirk Othmer, Encyclopedia of Chemical Technology Fourth Edition Vol. 22, P-947-55. Generally the electronic grade strontium carbonate is prepared using strontium chloride and any volatile precipitating agent. In the commercial process the strontium carbonate is precipitated by the CO2 or soda ash through SrS. Sulfur and Sodium contamination is observed in these processes which is not acceptable to the electronics applications. Particle size of the product reported was I to 2 micron whereas particle size required in electronics applications is 05 to 0 8 micron

OBJECTS OF THE INVENTION
An object of this invention is to propose a process for the preparation of electronic grade
strontium carbonate having the required purify.
Another object of this invention is to propose a process for the preparation of electronic
grade strontium carbonate having an improvement in the black ash process for the
recovery of water soluble strontium values.
Still another object of this invention is to propose a process for the preparation of
electronic grade strontium carbonate having an improved conversion efficiency.
DESCRIPTION OF THE INVENTION
According to this invention, mere is provided a process for the preparation of electronic
grade strontium carbonate which comprises in mixing thoroughly a reaction mixture
consisting of powdered celestite and industrial coke in powdered form, subjecting me
reaction mixture to reduction in a known manner to obtain water soluble SrS, dissolving
and carbonizing said SrS to obtain electronic grade strontium carbonate.
Accordingly the present investigation provides improvement in the black-ash process for
the recovery of water soluble strontium values from celestite ore which comprises mixing
thoroughly a reaction mixture consisting of powdered celestite ore and industrial coke,
reducing in known manner at a temperature in range of 400-950° C for a period of 1-2 hrs.
to obtain the water soluble Sr-values.
The powdered celestite used is of-100 + 140 mesh size, the powdered coke used is of
mean particle size -100 + 140 mesh.
The reduction reaction is affected by oxygen atmosphere or in open system, ie. in the
presence of air.
The improved process consists of mixing thoroughly the reaction mixture consisting of
celestite and industrial coke/coal. The mixed charge consists of celestite (with 98%

SrSO4) and stoichiometric amount of industrial carbon (62.5% C) in the form of coke fines. The chemical analysis of celestite and proximate analysis of industrial coke/coal sample is as given in Table 1.
TABLE-1 Analysis of Raw Materials
(Table Removed)
The reduction was carried out preferably in a vertically mounted tubular reactor at a temperature in the range of 400-950°C for a period of 1-2 hrs.. The reduction reaction carried out in strictly O2 free atmosphere. The yield of water soluble strontium was always 15-20% higher than the reported processes.

CARBONATE PRECIPITATION
The water soluble SrS prepared by the above black-ash process is used for preparation of electronic grade SrCO3. In this process the SrS was dissolved in hot water (70-80°C) The residue remaining alter dissolution was separated by nitration and washed 2-3 time with hot water. The total volume was adjusted in such a manner so that the final solution obtained contains ~ 20% wt/vol. of Sr-compound (SrS) The solution of SrS was then feed into the precipitation tank where 40% solution of NH4HCO3 is added to the SrS solution. The proximate analysis of ammonium bicarbonate is as given in Table.2
TABLE-2
Ammonium Bicarbonate

(Table Removed)

The following reaction takes place
2SrS + 2NH4HCO3 → 2SrCO3 + (NH4)2 S + H2S (4)
(liquid) (liquid) (ppt) (liquid) (Gas)
The precipitate of SrCO3 was formed in the precipitation tank After complete precipitation it was separated by filtration then washed with hot water 3-4 times The precipitate was then dried at 120°C to 3-4 his. The lumps obtained after drying, ground and analyzed by known volumetric as well as instrumental methods.
The proven advantages of improved process ( both the stages) & its practical significance are clear from the examples described, which are given to further illustrate the process and should not be construed to limit the scope of the present invention
EXAMPLES:
Example-1 : : lOgms of Celestite powder (-100+140)mesh size and 3.25 gm of Industrial coke of (-100+140)mesh size were mixed thoroughly and heated in a tubular furnace of internal dia. 75mm The temperature profile in the furnace was adjusted in the range of 400-950°C. The material is heated for one hr in the nitrogen atmosphere The reaction is quenched by taking out the material from the furnace. The cooled product weighed ( 6.61gms.) and analyzed for SrS content to find out the conversion efficiency of the reduction of SrSO4 to SrS It is observed that the conversion efficiency was 88-92% when the temperature of heating /one was maintained at 40()-950°C. The above
SrS is dissolved and carbonised to piepare electionic guide S1CO3. The overall conversion efficiency is found to be 85-92% This is the maximum conversion efficiency observed at that temperature and time i.e. 1 hr
Example - 2 : 50gms of Celestite powder (-100+140)mesh size and 16.25gm of Industrial coke of (-100+140)mesh size were mixed thoroughly . The temperature profile in the furnace was adjusted in the range of 400-950°C. The material is heated for one hr in the nitrogen atmosphere. The reaction is quenched by taking out the material from the furnace. The cooled product weighed (134.76gms) and analyzed for SrS content to find out the conversion efficiency of the reduction of SrSO4 to SrS. It is observed that the conversion efficiency was 88-92% when the temperature of heating zone was maintained at 950°C. The above SrS is dissolved and carbonised to prepare electronic grade SrCO3 The overall conversion efficiency is found to be 85-92% This is the maximum conversion efficiency observed at that temperature and time i.e. 1 hr
Example - 3 : 500gms of Celestite powder (-100+140)mesh size and l62 gm of Industrial coke of (-100+140)mesh size were mixed thoroughly and heated in a tubular furnace of internal dia 75mm The temperature profile in the furnace was adjusted in the range of 400-950°C. The material is heated for two hrs in the nitrogen atmosphere. The reaction is quenched by taking out the material from the furnace The cooled product weighed (315.2gms) and analyzed for SrS content to find out the conversion efficiency of the reduction of SrSO4 to SrS. It is observed that the conversion efficiency was 85-90% when the temperature of heating zone was maintained at 400-900°C. I he above SrS is dissolved and carbonised to prepare electronic grade SrCO3. The overall conversion efficiency is found to be 82-90%. This is the maximum conversion efficiency observed at that temperature and time i.e. 2 hrs.
Example - 4 : 1950gms Celestite powder of (-100 +140 ) mesh size and 645 gins of Industrial coke of (-100+140 ) mesh size were mixed thoroughly, and heated in tubular furnace. The temperature profile in the furnace was adjusted to 400-950°C The material is heated for 2 1/2 hrs in the nitrogen atmosphere. The reaction is quenched All other step are followed as per example 1. The cooled product weighed (1418gms) and analyzed for SrS content to find out the conversion efficiency of the reduction of SiS()( to SrS. It is observed that the conversion efficiency was 85-90% when the temperature of heating zone is maintained at 400-950°C. The SrCO3 is prepared as discussed in example 1 and weighed ( !209 gins ). The conversion efficiency for overall process i.e. BaSO4-BaCO3 is around 82-90%. This is the maximum conversion efficiency found at that temperature and time for this batch size (i.e.2 kg )


ANNEXURE-I: Specifications of Electronic Grade StrontiumCarbonate

(Table Removed)





WE CLAIM
1. An improved process for preparation of electronic grade strontium carbonate comprising of powdered celestite ore as hearein described, industrial coke, such as coal in powdered form, subjecting the reaction mixture to reduction preferably in a vertically mounted tubular reactor at a temperature of 400-950°C for a period of 1-2 hours in a oxygen free atmosphere to obtain water soluble SrS, said SrS was dissolved as herein described, and carbonazing to obtain electronic grade strontium carbonate.
2. An improved process as claimed in claim 1 wherein the powdered celestite and industrial coke is used of-100+140 mesh respectively.
3. An improved process for the preparation of electronic grade strontium carbonate substantially as herein described and illustrated in the examples.

Documents:

487-DEL-2002-Abstract-(16-09-2008).pdf

487-del-2002-abstract.pdf

487-DEL-2002-Claims-(16-09-2008).pdf

487-del-2002-claims.pdf

487-DEL-2002-Correspondence-Others-(16-09-2008).pdf

487-DEL-2002-Correspondence-Others-(28-01-2009).pdf

487-del-2002-correspondence-others.pdf

487-del-2002-correspondence-po.pdf

487-DEL-2002-Description (Complete)-(16-09-2008).pdf

487-del-2002-description (complete).pdf

487-DEL-2002-Form-1-(28-01-2009).pdf

487-del-2002-form-1.pdf

487-del-2002-form-18.pdf

487-DEL-2002-Form-2-(16-09-2008).pdf

487-del-2002-form-2.pdf

487-del-2002-form-3.pdf

487-DEL-2002-GPA-(28-01-2009).pdf

487-DEL-2002-Petition-137-(28-01-2009).pdf


Patent Number 231858
Indian Patent Application Number 487/DEL/2002
PG Journal Number 13/2009
Publication Date 27-Mar-2009
Grant Date 12-Mar-2009
Date of Filing 23-Apr-2002
Name of Patentee THE SECRETARY, DEPARTMENT OF INFORMATION TECHNOLOGY
Applicant Address ELECTRONICS NIKETAN 6 CGO COMPLEX NEW DELHI-110 003
Inventors:
# Inventor's Name Inventor's Address
1 B.B. KALE, CENTRE FOR MATERIALS FOR ELECTRONICS TECHNOLOGY, PUNE-411008
2 SONAWANE R S, CENTRE FOR MATERIALS FOR ELECTRONICS TECHNOLOGY, PUNE-411008
3 APTS S.K, CENTRE FOR MATERIALS FOR ELECTRONICS TECHNOLOGY, PUNE-411008
4 MATHUR A CENTRE FOR MATERIALS FOR ELECTRONICS TECHNOLOGY, PUNE-411008
5 SARNOT S L CENTRE FOR MATERIALS FOR ELECTRONICS TECHNOLOGY, PUNE-411008
PCT International Classification Number C01F 11/18
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA