|Title of Invention||
A PROCESS FOR THE PREPARATION OF ULTRA FINE ACTIVATED CALCIUM CARBONATE FROM INDUSTRIAL WASTE OF PHOSPHORIC ACID PLANT
|Abstract||The present invention provides a process for the preparation of ultra fine activated calcium carbonate from an industrial waste of phosphoric acid plant The present invention involves the treatment of crude and grey calcium carbonate with dil. HCL followed by neutralization with NaOH and subsequently re precipitated with calcium carbonate solution in the presence of chelating agent and dispersant. It provides a simple and precise method to utilise an industrial waste to synthesise a value-added material; ultra-fine glossy precipitated calcium carbonate having whiteness more than that of boric acid which is usually used as a standard for comparison of reflectance.|
|Full Text||FIELD OF THE INVENTION
The present invention relates to a process for the preparation of ultra-fine activated calcium carbonate with improved whiteness from an industrial waste of phosphoric acid plant.
BACKGROUND OF THE INVENTION
In normal practice phosphoric acid is produced industrially by the treatment of rock phosphate in nitric acid or sulphuric acid. However the grey and impure calcium carbonate is obtained as a waste/by product when phosphoric acid is produced from rock phosphate by the use of nitric acid, according to the following reaction.
Ca3(PO4)2 + 6HNO3 = 2H3PO4 + 3Ca(NO3)2 Ca(NO3)2 + (NH4)2CO3 = CaCO3 + 2NH4NO3
This crude calcium carbonate has 14 percent of water, 1.8% silica, 0.05% alumina, 0.05% iron oxide, 0.5%, metallic iron powder and 0.05%, magnesium oxide in its composition, with a wide range of particle size distribution. For each tonne of phosphoric acid manufactured, about 1.5 tonne of crude sludge is generated. The present use of the waste/sludge is as a soil conditioner, for neutralising waste acids in industries and manufacture of commercial bleaching powder. All these uses put together contribute to a negligible utilization of the sludge, still leaving a huge quantity for commercial exploitation. This sludge is reported to be posing serious disposal and pollution problems. In addition, demand for phosphate based fertilizer and phosphoric acid is increasing day by day which would result in accumulation of a large quantity of the sludge. One of the ways to deal with the problem is to synthesise ultra-fine and active precipitated calcium carbonate with whiteness of higher order which has commercial value.
Calcium carbonate is globally used as a raw material for expansion and dispersion, binding agent or filler in various consumer industries like paper, plastics, paint, polymers, synthetics, Pharmaceuticals, cosmetics, rubber and
ceramics etc. Precipitated calcium carbonate (PCC) with surface coating are specially designed for use in rigid and liquid polymers, natural and synthetic elastomers etc. In rigid PVC it functions as cost effective processing aid and also provides valuable improvements in final mechanical properties. In flexible PVC cables, their inclusion can significantly limit release of harmful gases to environment, on combustion.
Filler grade calcium carbonate can be produced by specific grinding of a natural calcium carbonate deposit based on chalk, lime stone or marble. The calcium carbonate based white pigments obtained by grinding of lime stone or marble are commonly known as ground calcium carbonate(GCC). For production of PCC, the current industrial practice involves burning of high grade calcium carbonate to calcium oxide. It is obvious that for the production of both PCC as well as GCC high quality natural calcium carbonate is a bare necessity. Especially, for PCC the choice is limited to high quality limestone.
The commercial grade PCC is produced in two forms; precipitated calcium carbonate and activated calcium carbonate. These two forms differ with respect to their coating, which the former does not have but the latter has. At present the total demand for quality grade PCC, coated or uncoated, far exceeds its total production. Moreover there is a tremendous possibility for growth of paper, polymer and pigment industries where it is used as a filler.
Keeping the above industrial scenario in view, investigations were carried out for the development of a process to synthesise PCC from crude and grey calcium carbonate, obtained as a waste in phosphoric acid plant.
The applicants have developed a process wherein crude and grey calcium carbonate obtained as a by-product/waste in phosphoric acid plant is dissolved in dilute hydrochloric acid, filtered and the filtrate is treated with an alkali carbonate in the presence of a particle size modifier and a surface coating material under vigorous stirring condition, resulting in the formation of an active PCC, which is filtered, washed with water till free from soluble impurities and finally dried.
Reference can be made to US patent no. US2003099591 by jasra raksh vir (in); oza pravinchandra mahasukhray (in); somani rajesh shantilal (in); chunnawala jatin rameshchandra (in); sheth mrunal vinodbhal (in); thakkar vikram vinodrai (in); badheka yogiraj mansukhlal (in); ayyer jayalekshmy (in); patel virendra bhikhabhai (in), an environmental friendly process for the production of finely divided calcium carbonate suitable for industrial application from calcium rich by-product of nitrophosphate fertiliser plant by adopting purification steps of thermal treatment, pulverization and coating using emulsion of fatty acid or its derivatives.
Another reference can be made to CN1100067 Precipitated calcium carbonate preparation using waste from dicyandiamide plant, Zhikang tu , the method discloses the precipitation of calcium carbonate using industrial waste of dicyandiamide includes removing impurities of water, sand, nitrogen-containing organic matter by dewatering, baking and screening to obtain carbon-containing precipitated calcium carbonate, and purifying by combustion decarbonating process to separate free carbon, to obtain high-purity precipitated calcium carbonate, which may be used as filler in rubber, plastics, paint, paper and insulating material productions.
At present, as per the prevailing industrial practices, PCC is manufactured from suitable grade lime stone containing more than 90 percent of calcium oxide by controlled chemical reactions; calcination of lime stone to obtain burnt lime, mixing with water to form a thin slurry containing 15-20 percent of calcium hydroxide and bubbling of carbon dioxide through the slurry from a compressor in a carbonating tower to produce PCC.
The drawback of the above process is that it utilizes only high pure limestone containing more than 90 percent of calcium oxide but in the present investigation, an industrial waste is used as the raw material and the steps involved do not require any sophisticated technology.
A simple method is developed for the preparation of ultra-fine active PCC with quality white ness which can be used as filler in paper industry for the
preparation of wood free uncoated paper to give it a reflectance value of higher order. Since it has been surface treated, it can be used in rigid and liquid polymer, natural and synthetic elastomers where they bring improvements in tear and tensile properties better than that with standard extenders.
Crude calcium carbonate, grey in colour, having varying compositions of silica, iron oxide, metallic iron, alumina and magnesium oxide, is generated in the phosphoric acid plant, when rock phosphate is treated with nitric acid. This is agitated with water by a magnetic stirrer, followed by rejection of the washings and separation of the metallic iron powder sticking to the magnetic paddle. Subsequently it is dissolved in dil HCI, filtered, neutralised, treated with solutions of EDTA for chelating of calcium ions to slow down the rate of precipitation and poly vinyl alcohol(PVA) or sucrose solutions which act as dispersants to avoid coagulation of the precipitate and activate it by forming a coating, followed by addition of solution of Na2CO3 to synthesise precipitated calcium carbonate(PCC).
The novelty of this method is that it provides a simple and precise method to utilise an industrial waste to synthesise a value-added material; ultra-fine glossy precipitated calcium carbonate having whiteness more than that of boric acid which is usually used as a standard for comparison of reflectance.
OBJECTS OF THE INVENTION
The main object of this method is to provide ultra-fine activated calcium carbonate with improved whiteness from an industrial waste of phosphoric acid plant.
Another object of this method is to prepare PCC from crude, grey and impure calcium carbonate, obtained as an industrial waste.
Still another object of this process is to prepare ultra-fine PCC with superior whiteness and high order covering power which can partially or totally replace titanium dioxide as a white pigment.
Yet another object of this method is to prepare surface treated active PCC which finds applications in rigid and liquid polymers as well as natural and synthetic elastomers to enhance their mechanical properties.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a process for the preparation of ultra fine activated calcium carbonate from an industrial waste of phosphoric acid plant, which comprises washing the crude and grey calcium carbonate obtained from the industrial waste with water and treating it with dil.HCI, followed by filtration to obtain the calcium chloride solution, neutralizing the resultant calcium chloride solution with about 10% aqueous NaOH solution, followed by adding about 100ml ethylene diamine tetra acetic acid (EDTA) solution, as a chelating agent, under stirring, further adding dropwise about 1 molar aqueous sodium carbonate solution optionally with about 10% (v) aqueous solution of sucrose or about 5% polyvinyl alcohol, as dispersants, simultaneously to the above said resultant solution, at a temperature in the range of 25°C to 35°C, under stirring, for a period of about 1hr to precipitate out the calcium carbonate, washing, purifying and finally drying the resultant precipitate by known method to obtain the desired product.
In an embodiment of the present invention the calcium carbonate obtained has an average particle size ranging between 2-5 microns.
In another embodiment of the invention the calcium carbonate obtained has the average particle size of 2-3 microns when only EDTA is used in the reaction mixture.
In yet another embodiment of the invention the calcium carbonate obtained has the average particle size of 19-20 microns when EDTA & sucrose are used in the reaction mixture.
In still another embodiment the calcium carbonate obtained has the average particle size 5-6 microns when EDTA and polyvinyl alcohol is used in the reaction mixture.
The essential steps involved in the process are
(a) Washing a slurry of industrial waste crude and grey calcium carbonate
with water by stirring with a magnetic stirrer, decantation of the washings
and separation of the metallic iron sticking to the magnetic paddle.
(b) Dissolution of the washed sample in dilute hydrochloric acid.
(c) Treatment of the sample solution with EDTA by stirring.
(d) Mixing of the sample with poly-vinyl alcohol or sucrose solution by stirring.
(e) Drop wise addition of sodium carbonate solution to the solution of the
sample along with stirring.
(f) Ageing of the PCC by stirring for two hours.
(g) Filtration and drying of the PCC.
100 grams of crude and grey calcium carbonate was agitated with 500 ml. of water by a magnetic stirrer for half an hour, allowed to settle, the washing was rejected and the metallic iron powder sticking to the paddle was cleaned and rejected. The washed sample was dissolved in 1000ml. of dil HCI(2N), filtered and a stock solution of 1L was prepared.
The following examples are given by the way of illustration and therefore should not be construed to limit the scope of the invention.
200 ml. of the above prepared calcium chloride solution(A) was taken in a reaction vessel, neutralised by addition of NaOH(10%) solution, (indicated by the appearance of a faint precipitate, pH= 9.5), followed by addition of 100 ml. of EDTA solution(O.IM) and kept stirred. 210 ml. of Na2CO3 solution (1M) was
added drop wise from a separating funnel over a duration of 40-45 minutes at 30±2°C and stirring continued for one hour. The precipitated calcium carbonate thus formed was settled and washed by decantation. The process of stirring with 500 ml of water, settling and washing by decantation continued for three times and finally it was with acetone, filtered and dried at 110°C for two hours. 18.5 grams of PCC was obtained.
200 ml. of the above prepared calcium chloride solution(A) was taken in a reaction vessel, neutralised by addition of NaOH(10%) solution, (indicated by the appearance of a faint precipitate, pH= 9.5), followed by addition of 100 ml. of EDTA solution(O.IM) and kept stirred. 210 ml. of Na2CO3 solution (1M) and 100 ml of sucrose solution(10%) were added drop wise from two different separating funnels simultaneously over a duration of 40-45 minutes at 30±2°C and stirring continued for one hour. The precipitated calcium carbonate thus formed was settled and washed by decantation. The process of stirring with 500 ml of water, settling and washing by decantation continued for three times and finally it was washed with acetone, filtered and dried at 115°C for two hours. 18 grams of PCC was obtained.
200 ml. of the above prepared calcium chloride solution(A) was taken in a reaction vessel, neutralised by addition of NaOH(10%) solution, (indicated by the appearance of a faint precipitate, pH= 9.5), followed by addition of 100 ml. of EDTA solution(O.IM) and stirred. 210 ml. of Na2CO3 solution (1M) and 20 ml of poly vinyl alcohol solution(5%) were added drop wise from two different separating funnels simultaneously over a duration of 40-45 minutes at 30±2°C and stirring continued for one hour. The precipitated calcium carbonate thus formed was settled and washed by decantation. The process of stirring with 500 ml of water, settling and washing by decantation continued for three times and finally it was washed with acetone, filtered and dried at 110±5°C for two hours. 18 grams of PCC was obtained.ADVANTAGES OF THE INVENTION
1. The present invention provides a method to solve the disposal problem of
an industrial waste
2. Development of a simple method for the preparation of pure precipitated
calcium carbonate from an industrial waste of phosphoric acid plant.
3. The precipitated calcium carbonates prepared in this process have an
average particle size between 2-3 microns, when prepared in EDTA
medium, 19-20 microns, when prepared in a medium of EDTA and
sucrose, and 5-6 microns when prepared in a medium of EDTA and poly
vinyl alcohol, with narrow ranges of size distributions. This can be further
reduced by pulverisation.
4. The purity of PCC prepared in all the above three methods are more than
5. The calcium carbonates prepared by these methods are made active by
surface coating with poly-vinyl alcohol/sucrose and can be used in
polymer industries to improve impact performances of rigid and liquid
polymers, as well as elastomers.
6. They exhibit reflectance value of very higher order i.e. more than that of
7. Their ultra-fine sizes and excellent reflectance property and purity can
achieve increased coverage of base paper, when used as filler in paper
8. As a white pigment they can partially or totally replace titanium dioxide.
|Indian Patent Application Number||910/DEL/2006|
|PG Journal Number||44/2013|
|Date of Filing||30-Mar-2006|
|Name of Patentee||Council of Scientific and Industrial Research.|
|Applicant Address||ANUSANDHAN BHAWAN, RAFI MARG, NEW DELHI - 110 001, INDIA.|
|PCT International Classification Number||C01F 11/18|
|PCT International Application Number||N/A|
|PCT International Filing date|