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Topic Name: Laboratory Scale Production of Commercial Grade Calcium Carbonate from Lime-Soda Process
Category: Chemical
Research persons: MS Islam, AKMA Quader
Location: DHAKA, Bangladesh
Details
Quality precipitated calcium carbonate has much demand in
various chemical and allied industries as filler,
surface coating, whitening, adhesive etc. A study was carried
out by modifying classical lime-soda process
to obtain high quality precipitated calcium carbonate. The
experiments were carried out in two stages
using commercial and analytical grades of sodium carbonate and
lime as reactants. After causticization, the
filtrates from the washing of calcium carbonate were used to
prepare all solutions for reactions in next
stage. The precipitated calcium carbonate obtained from the
process was analyzed and comparisons were
made with the commercially available precipitated calcium
carbonate produced from carbonation method.
The calcium carbonate produced from causticization was superior
to those produced by carbonation
method in the country. The crystal structure of carbonate was
calcite.
Precipitated calcium carbonate is one of the most versatile
mineral fillers and is used in a wide
range of products including paper, paint, plastic,rubber, ink,
textiles, chalks, sealants, adhesives etc.
United States Pharmacopoeia (USP) grades are used in
dentifrices, cosmetics, foods and pharmaceuticals. Crescent
Chemicals Ltd. and Usha Chemicals Ltd. are the producers of
precipitated calcium carbonate in Bangladesh. The total
production capacity of these plants is 20,000 tonnes per year
against yearly consumption of 44,000
tonnes and the rest 24,000 tonnes per year of calcium carbonate
is imported. Precipitate Calcium carbonate can be
producedby several methods such as :
a. Carbonation Method
b. Calcium Chloride-Sodium Carbonate
Double Decomposition Method:
c. Lime-Soda Method
The carbonation method is the unique method of calcium carbonate
production to-day and is
widely used commercially. The lime-soda process is the classical
methodof producing caustic soda. In this process, a
solution of sodium carbonate is treated with excess calcium
hydroxide producing liquid caustic and byproduct
precipitated calcium carbonate. The quality of precipitated
calcium carbonate formed in this
process is not good replacement of commercial precipitated
calcium carbonate. The byproduct
calcium carbonate is handled in three following different ways :
• “reburned” in rotary kilns to recover
lime
sent to cement plant for use as one of its
main raw materials of cement
• disposed as waste when
it cannot be sold or used
The present yearly demand for caustic soda and chlorine in
Bangladesh are 80,000 tonnes and 3600
tonnes respectively. The demand for chlorine is being met
locally while the production capacity of
caustic soda in the country is only 20,000 tonnes per year. The
rest 60,000 tonnes of caustic soda per
year are imported . Because of limited demand of chlorine, the
growth of chlor-alkali industry in
Bangladesh has been stopped. Considering reality (attractive
demand of caustic soda and calcium
carbonate) in Bangladesh, lime-soda process can be the right
route for making caustic soda as it requires
less investment per unit capacity. The profitability of
lime-soda process can be
made attractive by improving the quality of the byproduct
precipitated calcium carbonate and its
efficient recovery. White colour, low alkalinity, free from
harmful impurities and non abrasiveness are
some prime requisites of calcium carbonate for use
as a whitening, filler and coating. If byproduct precipitated
calcium carbonate can be produced in
such form by modification of the conventional process, the
process can be commercially exploited.
This paper deals with obtaining quality precipitated calcium
carbonate from modified limesoda
process which involves two stage reaction for completing
conversion of soda ash to caustic soda.
REFERENCE :
Chemical Engineering Research Bulletin ISSN Print:0379-7678 Online:2072-9510
ABOUT THE RESEARCHER :
MS Islam
Department of Chemical Engineering, Bangladesh University of Engineering &
Technology, Dhaka-1000, Bangladesh
AKMA Quader
Department of Chemical Engineering, Bangladesh University of Engineering &
Technology, Dhaka-1000, Bangladesh
| Tags: |
calcium carbonate - chemical - allied industries - filler - surface coating - whitening - adhesive - lime-soda process - analytical grades - sodium carbonate - lime - reactant - causticization - - |
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