|Title of Invention||
"A PROCESS FOR THE PRODUCTION OF ZINC POWDER."
|Abstract||In the process of present invention zinc powder is produced through electrolytic process wherein the anode is taken as zinc dross which is abundantly available and cheaper than pure zinc sheet or pure zinc ingot and the cathode is either zinc sheet, Titanium or stainless steel which is again cheaper than Nickel and Magnesium used in alkaline bath of earlier process. In the present invention, chloride bath contains zinc chloride, ammonium chloride, potassium chloride. The chloride bath is also cheaper than the alkaline bath. The % of zinc powder yield in optimum condition in chloride bath is 85 - 90%.|
|Full Text||The present invention relates to a process for the production of zinc powder. The invention particularly relates to a process for the production of zinc powder from zinc dross which is available abundantly from hot dip galvanizing plant The invention will be useful for production of zinc power at a low cost which is used in paint industry for making protective paints to prevent atmospheric corrosion by applying on steel substrates.
Zinc powder is generally produced in substantial quantities by distillation-condensation method reference may be made to 'Zinc Waste and their Utilisation1, NML Tech. Jr. Nov. 1968 wherein zinc is recovered from zinc dross by distillation at noo°c.
In an another method zinc powder is produced by reduction of zno with carbon. Reference may be made to Powder Metallurgy by John Wulf, American Society for Metals, Ohio, 1942 wherein zno processed to eliminate excess Oxygen which is present in the reaction vessel . The CO2 normally forms in the reduction process during reaction which prevents further oxidation of the powder.
In yet another process for zinc powder production is through atomization process. The atomization process involves a melting furnace and refactory pot where melted zinc is kept. Through sucking and pressing through nozles of different diameter, the melted zinc is sprayed over a water tank and zinc powder is collected from the water. Because of oxidation and incontact with moisture the purity of zinc powder thus produced is less than 85 %.
In still another process the zinc powder is produced through electrolytic process. in this process the anode is taken as pure zinc sheet or pure zinc ingot and the
bath is alkaline one containing sodium hydroxide and sodium zincate with suitable amount of current density .
The hitherto known processes for production of Zinc powder by distillation -condensation, reduction and atomization as mentioned above are associated with high temperature, pressure along with atmospheric pollution . These processes are expensive and require skilled labours due to risk of explosion , fume generation and sound pollution whereas the zinc powder produced in electrolytic process using alkaline bath avoids all the drawbacks in the processes mentioned above which were present in the conventional process.
in the electrochemical route of using alkaline bath has advantage over the conventional pyrometallurgical processes, it's disadvantage of using Nickel and Magnesium as electrodes due to cost of Nickel or Magnesium is appreciably high and the bath reagents sodium hydroxide and sodium zincate are costly . Pure zinc sheet or pure zinc ingot is too costlier.
The main object of the present invention is to provide a process for the production of zinc powder from zinc dross which obviates the drawbacks as detailed above including electrochemical route using alkali bath .
in the process of present invention the anode is taken as zinc dross which is abundantly available and cheaper than pure zinc sheet or pure zinc ingot and the cathode is either zinc sheet, Titanium or stainless steel which is again cheaper than Nickel and Magnesium which is usually used in alkaline bath . in the present invention , chloride bath contains zinc chloride, ammonium chloride , potassium chloride etc. The chloride bath is also cheaper than the alkaline bath. The % of zinc powder yield in optimum condition in chloride bath is 85-90%. wherein
alkaline bath it is 75 - 80%. In the process of present invention it is possible to deposit the metal on the cathode surface in an electrolytic cell as powder or at least in a form in which it can be easily disintegrated mechanically into powder by suitable adjustment of the chemical and physical parameters.
Accordingly the present invention provides an improved process for the production of zinc powder which comprises
a. preparing an anode made up of zinc dross and a cathode selected
from a group comprising of stainless steel, zinc or titanium,
b. dipping the obtained cathode and anode in a chloride electrolytic bath
consisting of 30 - 75 g/l zinc chloride, 10-20 g/l sodium chloride, 2-5
g/l potassium chloride , and balance magnesium chlorides, maintaining
the temperature of said electrolytic bath in the range of 20 - 40°C, at a
pH ranging 5.5 to 6.5,
c. supplying direct current (DC) to the said electrolytic bath in the range of
5 - 15 Amps and voltage in the range of 1.5 to 8 V for the formation of
zinc powder onthe surface of the cathode and recovering the zinc
powder by conventional method , the said process characterized in that
use of chloride bath with anode made up of zinc dross.
In an embodiment of the present invention the temperature of the electrolytic bath may be maintained in the range of 20 to 40°C.
In another embodiment of the present invention pH of the electrolytic bath may be controlled in the range of 5.5 to 6.5.
In still another embodiment of the present invention the anode used may be of zinc dross or zinc sheet and cathode may be of steel, zinc and titanium.
In yet another embodiment of the present invention the yield and purity of zinc powder may be in the range of 85 to 90% and 97 - 98% respectively.
The invention is illustrated with the following examples which should not be construed to limit the scope of the invention .
EXAMPLES • 1
The experiment was carried out with working cell where the electrodes were zinc dross and pure zinc sheet . The later acted as cathode . The bath solution composed of zinc chloride 3% , sodium chloride 3% , potassium chloride and Borax added appropriately in distilled water. The pH adjusted to 5.5 at a temperature of 40 °c . A rectifier was used to supply DC. Ammeter, volt meter were connected in series & parallel with the working cell for recording current and voltage respectively . When the supply of current resumed , instantly deposition of powder on the cathode occurred .
The product was a loosely adherent spongy type which was easily scrapped through or brushed - off from the cathode , washed , treated with the passivator, dried and stored in packed sealed condition . The yield was 80% zinc powder .
EXAMPLE • 2
The apparatus consisted of electrochemical cell where zinc dross as anode and Titanium as cathode were used . The cell was connected to rectifier. Ammeter and volt meter were kept in series and parallel respectively with the cell for measuring current and voltage. The bath solution consisted of 3% zinc sulphate , 1.5 % zinc chloride and Borax in appropriate quantity in distilled water . The bath solution was homogenized with the help of a stirrer . pH adjusted to 6.5 and the temperature maintained at 30°c . Current and voltage measured from the ammeter and volt meter respectively . The deposition of zinc powder on the surface of the cathode began when the current supplied to the electrolytic cell started . The powder collected , washed with water , rinsed with solvent and finally treated with passivator, dried and stored in packed sealed condition .
The yield was 85% zinc powder.
EXAMPLE - 3
The experimental set up consisting of zinc dross as anodes , stainless steel as cathode and bath solution in a cell. A rectifier was used with experimental set up to supply the necessary direct current (DC) which was indicated by the ammeter and corresponding voltage was measured by volt meter . The working cell , ammeter were connected in series and voltmeter was in parallel. The bath solution comprised of 6% zinc chloride , 2% sodium chloride and ammonium chloride in distilled water. pH was maintained at 6.0 and temperature controlled at 30°c . 5 Amps current was supplied to the working cell through rectifier and powder deposition started on the surface of the cathode. The powder scrapped , filtered , dried and processed for storage. The yield was 90 % zinc powder.
1. The process is economical than conventional method as the main raw material is
the waste product.
2. The product is usually of high commercial purity with flaky powder
3. A considerable range of fitness of powder can be obtained by varying
4. The product has excellent sintering properties
5. Zinc dross used as the raw material is available at low cost
6. The process is free from atmospheric pollution
7. The process has no high temperature involvement
8. The process does not require sophisticated instruments
9. The process is non-cumbersome and easy to operate
10. It is eco-friendly.
1. An improved process for the production of zinc powder which comprises
a. preparing an anode made up of zinc dross and a cathode made
up from metal or alloy selected from stainless steel, zinc sheet
b. dipping the obtained cathode and anode in a chloride electrolytic
bath consisting of 30 - 75 g/l zinc chloride, 10-20 g/l sodium
chloride, 2 - 5 g/l potassium chloride , and balance magnesium
chlorides, maintaining the temperature of said electrolytic bath in
the range of 20 - 40°C, at a pH ranging 5.5 to 6.5,
c. supplying direct current (DC) to the said electrolytic bath in the
range of 5 - 15 Amps and voltage in the range of 1.5 to 8 V for the
formation of zinc powder on the surface of the cathode and
recovering the zinc powder by conventional method , the said
process characterized in that use of chloride bath with anode
made up of zinc dross.
2. An improved process as claimed in claim 1 wherein the yield of the zinc
powder is 90% and in the purity range of 97 - 98%.
3. An improved process for the production of zinc powder substantially as
herein described with reference to the examples.
|Indian Patent Application Number||1400/DEL/1999|
|PG Journal Number||50/2007|
|Date of Filing||22-Oct-1999|
|Name of Patentee||COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH|
|Applicant Address||RAFI MARG, NEW DELHI-110 001, INDIA.|
|PCT International Classification Number||C22B 4/00|
|PCT International Application Number||N/A|
|PCT International Filing date|