Title of Invention


Abstract The present invention relates to a process for converting metallic zinc, zinc dross, zinc ash and horn, zinc hydroxide, zinc ores or any other form of zinc in metallic or impure oxide form to zinc oxide by converting them to acid salt solutions, purifying them and passing Ammonia gas to directly precipitate out zinc oxide.
Full Text FORM 2

[39 OF 1970]
1 TITLE "Manufacture of Zinc Oxide -A 'New' Process"
NAME Mr. Umaprasad Mahapatra
ADDRESS 10/1, GEETA Society, Charai,
Thane - 400601, Maharashtra, India

The following specification particularly describes the nature of the invention and the manner in which it is to be performed:-

Field of the Invention
The present invention relates to a new process for making metallic oxides namely, zinc oxide.
The primary function of this process is to convert metallic zinc, zinc dross, zinc ash and horn, zinc hydroxide, zinc ores or any other form of zinc in metallic or impure oxide form to zinc oxide by converting them to acid salt solutions, purifying them and passing Ammonia gas to directly precipitate out zinc oxide.
Background of the Invention
In the present day practice of making metallic oxide namely, zinc oxide can be broadly classified in to three types:-
1) Direct process also known as 'American' process
In the 'American' process calcined zinc ore or impure zinc oxide is reduced in a furnace by carbon by application of electrical energy or by heat energy from burning fuel oil or carbon. The ensuing zinc vapours along with other gases is burnt in a chamber to yield zinc oxide.
In this process mention can be made of Sterling process, St. Joseph process, grate process and blast furnace process of imperial smelting for making zinc oxide and metal, mention can be made of my Indian Patent No. 142474 of 1975 in which reduction and oxidation were done in the same furnace.
2) Indirect process also known as 'French' process
In the 'French' process, pure zinc is boiled in retorts on crucibles, and vapours of zinc are oxidized, sucked by exhaust fans in to bag houses and then collected.
3) Wet process also known as 'secondary' zinc oxide
In this process, by product zinc hydroxide and carbonates are washed and calcined to zinc oxide.
4) Transparent grade zinc oxide
Mention can be made of yet another process of manufacture of extra fine particle size zinc oxide known as 'transparent' grade in commerce. Here dilute solution of sodium zincate is treated with carbon-di-oxide or hydrolyzed to obtain zinc oxide, which is filtered, washed and then dried. Due to high cost it is made in small quantities and for special applications only.

The successful technology of making good grade of zinc oxide mainly depends on the following factors:-
a) Raw material
b) Purity of zinc oxide produced
c) Size and shape of particles & bulk density
d) Investment and cost of production
e) Pollution and process control
Details of various processes are known fact and bulky literature are available and we will attempt only to describe this invention for its uniqueness and advantages compared to other known processes.
The direct process (No.1) can be generally classified as thermal process and needs quality raw materials with limits on lead and cadmium etc. They produce zinc oxide with contamination of carbon, sulphur and may need washing, calcining and grinding for acceptability. They are less bright than French process zinc oxide and usually unsuitable for Pharmaceutical application. They need huge investment in control of raw material, has difficulty in control of size and shape of particle and prone to heavy pollution. Due to non-availability of quality zinc concentrates of carbonate type many units have closed down in USA, China & Europe.
The indirect process (No.2) or French process the cost of production is high as it uses pure metal*. To reduce this cost some use mixture of metal and dross sacrificing quality as the zinc oxide carries part of the lead and iron with it. The process uses fuel oil and consumable retorts and crucible. Part of the metal is lost as zinc horn and zinc ash. However with metal, high purity zinc oxide with high brightness can be got. The only control on process is the burning rate, by control of combustion but some products contain metallic particles which have missed burning.
The process (No. 3) is generally known as secondary zinc oxide is based on bye product zinc hydroxide or carbonate from sodium hydrosulphite industry. The product has limitation as it is yellowish colour and heavy. This is because of calcinations and due to grain growth of zinc oxide leading to huge bulk density.
Summary of the Invention
This invention has been possible due to critical analysis and experiments against old beliefs and assumptions as follows:
1 That only zinc oxide made above 1300°C is white and below that is yellowish.
2 Ammonia gas bubbled into acid salt of zinc e.g. Zinc sulphate will produce zinc hydroxide and subsequent calcinations will produce heavy and yellowish zinc oxide.

After careful study of free-energy of formation of the reactions of the type
1 ZnS04 + 2NH3 + H20 = ZnO + (NH4)2S04 2. ZnCI2 + 2NH3 + H20 = ZnO + 2NH4CI
And by number of experiments it was found that colour of zinc oxide does not depend on the temperature of formation. The white colour is due to extreme fineness of particle size, orientation, purity & freedom from surface adsorption of impurities." Injection of ammonia gas alone or ammonia gas with air or steam into purified zinc sulphate, zinc chloride, zinc nitrate, zinc acetate or any other zinc acid salt or mixtures of above produces zinc oxide directly and that :
1. The particle size depends on dilution of the solution, rate and quantity of ammonia gas injected.
2. Exceptionally fine particles with very high brightness is possible
3. The purity of the product depends on the purity of zinc acid salt solution. The best choice is zinc sulphate.
4. The raw material can be with any impurities and the cheapest can be used.
5. The by-product ammonium sulphate is a valuable fertilizer and reduces the cost of production.
6. The ammonia gas can be regenerated from the by-product ammonium sulphate and re-cycled by treating it with lime.
7. There is no emission to atmosphere, no high temperature or fuel is used and there is no discharge of effluents and hence the process is ' pollution free'.
The filtered and washed zinc oxide can be simply dried, or further heated for densification and can be pelletized or surface treated as per standard commercial practice.
This invention offers a simple method of making "quality' zinc oxide from any zinc bearing material. It is fast, easy to operate and pollution free. The particle size, bulk density, purity and brightness can be easily controlled.
Detailed Description of Preferred Embodiments
This invention will now be described by way of illustration but not by way of limitation.
1) Any zinc acid salt solution such as sulphate, chloride, nitrate or mixtures there of can be used. The solution of zinc salt is purified by usual commercial practice by zinc dust or zinc oxide. The solution should not be very concentrated or dilute. In the first case zinc ammonium sulphate may form and will need further dilution, and the ammoniation continued. In the latter case very find particle size will lead to fluffy zinc oxide which has to be corrected by densification.

2) The reaction is carried out in the following steps:-
A reactor is chosen so that it has no reaction with zinc salt solution i.e. either stainless steel, rubber lined, monel or plastic or any other suitable material of construction. The reaction vessel can be round, square or any other shape, open or closed at top, with or without a stirrer. Ammonia gas with or without air / steam can be injected, through single or multiple tubes of SS, glass, rubber or any other corrosion proof material of suitable diameter or section, solely dependant on design considerations; described here as an illustration and not by way of limitation. The injection pipes will have non-return valves and liquid traps to prevent liquid from the reactor being sucked back to the ammonia gas container, when the gas is exhausted. There shall be ammonia gas 'leakage' detectors in appropriate positions. The supply of ammonia gas from cylinders, tankers or recovered ammonia gas vessel is regulated by valves. All necessary safety measures are provided for in case of emergency. The process end-point is indicated by slight excess ammonia gas at top of the reaction vessel.
The ammonia gas is stopped for few minutes or switched over to second reaction vessel. After few seconds the precipitate of zinc oxide will start settling. The top liquid is drawn and tested outside by passing ammonia gas and if there is reasonable precipitation, the ammonia gas injection is continued. If by chance excess ammonia gas has been injected, a calculated or estimated amount of zinc sulphate is added. The extra absorbed ammonia will react with the zinc sulphate to yield zinc oxide.
The by-product ammonium sulphate, ammonium chloride, ammonium acetate, etc, will have a tendency to absorb small quantities of zinc oxide, which can be recovered after filtration and usual techniques. If the ammonia is to be re-cycled by adding lime then the small quantity of zinc oxide dissolved in ammonium sulphate, chloride or acetate may be ignored.
3 The zinc oxide and ammonium sulphate solutions are separated by Neutche filter, centrifuge, filter press or any other filtration process. The ammonium sulphate solution is pumped to its storage tank, to either be crystallized or to recycle the ammonia gas. The zinc oxide precipitate is preferably washed with hot water to remove any absorbed gas and again filtered after thorough washing.
4 The wet zinc oxide cake is dried in any commercial type drier with a temperature range of 105 to 500°C, preferably at 250°C. If densification of the product is desired a higher temperature of up to 500°C can be used. The final product is a fine powder but usually passed through a hammer mill to increase the brightness.and uniformity. The product is weighed and packed.
5 The filtrate like ammonium sulphate, chloride, nitrate and acetate are either purified and crystallized for sale or decomposed with calcium hydroxide and the ammonia gas recovered and recycled.

1 Commercial zinc sulphate was taken and made in to solution of medium concentration. To remove iron and lead little hydrogen peroxide was added and the solution was boiled. A little zinc oxide (zinc dust can also be used) was added to remove iron and other impurities. The filtered solution was placed in a cylindrical stainless steel vessel and ammonia gas was passed in to the solution by a rubber pipe which in turn was attached to a glass tube. Zinc oxide started precipitating and no clogging of the glass tube was observed. There was no smell of ammonia gas on top of the vessel. The gas injection was stopped when the whole solution appeared to be colloidal. Slowly the zinc oxide precipitated and ammonia gas was injected again till a faint smell of ammonia and the solution was filtered to remove zinc oxide, which was thoroughly washed and dried in a oven at 150°C. The zinc oxide tested above 99.8% and the yield was above 98%. The filtrate of ammonium sulphate was converted to ammonia alum.
2 In another preferred embodiment a purified 50% zinc chloride solution was taken in a polyvinylchioride vessel and the experiment was carried out by injecting ammonia gas from an ammonia gas cylinder, and a bright white grade zinc oxide was produced. It needed more washing to remove last traces of chloride and some zinc oxide was dissolved in ammonium chloride. The yield was above 95%. Small amount of zinc oxide was recovered while crystallizing ammonium chloride which was recycled in the next experiment.
3 In another preferred embodiment an equal mixture by weight of zinc sulphate and zinc acetate was used in a stainless steel vessel with stirring arrangement while passing ammonia gas. High purity zinc oxide with high yields was obtained. The by-product mixture of ammonium sulphate and acetate was used for generating ammonia gas for the next trial.

I Claim:-
1 A process for the manufacture of zinc oxide using zinc in form of metallic granules, dust, dross and the like and any zinc containing compounds like calcined ores and ashes by first converting them to neutral acid salt solution like sulphates, chlorides, nitrates, acetates, etc but preferably sulphate and purifying them to remove impurities and injecting gaseous ammonia with or without air/steam to directly obtain pure zinc oxide in form of a precipitate.
2 A process is claimed in claim I, incorporating injection of ammonia gas in to neutral zinc acid salt in a corrosion resistant vessel of cylindrical, rectangular or any polygonal section and height as required by design.
3 A process is claimed in 1, using any raw material, with any impurities by first converting in to any acid salt and removing any impurities such as iron, lead, cadmium, etc by well known and as practised in zinc electrolytic process.
4 A process as claimed in claim 3, the zinc acid salt solution is neutralized before injecting ammonia gas, to avoid excess use of gas.
5 A process as claimed in claim 4, the dilution of acid salt solution is predetermined as per the fineness of particles desired.
6 A process as claimed in claim 5, the rate of injection of ammonia gas with or without air/ steam is pre-determined in relation to particle size desired in the final product.
7 A process as claimed in claim 6, is essentially carried out at ambient temperature.
8 A process as claimed in claim 7 needs no heating or cooling during the injection of ammonia gas.
9 A process as claimed in claim 8 minor adjustments in controlling temperature is done by stopping injection of the gas for short periods.
10. A process as claimed in claim 9 there is a provision of non-return valve and liquid trap to prevent contents of reaction vessel from entering the ammonia gas container when vacuum is created when the gas is exhausted.

11 A process as claimed in 10, adequate provision is made for prevention of accidents by providing devices for detecting leakage of ammonia gas and its prevention.
12 A process as claimed in 11, a second reactor with neutral acid salt solution of zinc is kept ready, so that when the ammonia gas injection reaches end-point, it can be switched on to it, with no need to stop the gas injection.
13 A process as claimed in claim 12, when the end-point is reached and there is faint smell of gas or by means of the gas indicator the injection of gas is stopped or switched to second reactor. A sample of the solution is filtered and tested for further precipitation of zinc oxide by ammonia gas. If required the injection of ammonia gas is continued but if precipitate is negligible, the injection of gas is stopped and solution of ammonium salt with zinc oxide is allowed to settle.
14 A process as claimed in claim 13, if an excess of ammonia gas has been injected, it is reacted with an estimated quantity of zinc acid salt solution e.g. zinc sulphate for neutralization of excess ammonia gas.
15 A process as claimed In claim 14, the zinc oxide in the reaction vessel is allowed to settle, while the injection of ammonia gas is started in vessel no.2. There is no limitation to the number of reaction vessels to be used but is a matter of convenience.
16 A process as claimed in claim 15, the precipitated zinc oxide is filtered in neutche filter, centrifuge, filter press or any other filtration equipment and thoroughly washed preferably with hot water for removal of the absorbed ammonia gas before sending it to the drier.
17 A process as claimed in claim 16, the washed and filtered precipitate of zinc oxide is dried in any suitable commercial drier with a range from 105 to 500°C but preferably at 250°C. The higher temperature is used if the densification of the product is desired, by grain growth.
18 A process as claimed in claim 17, the dried zinc oxide is preferably passed through a hammer mill for uniformity of the product and increase in brightnessl though not essential. The product is then weighed and packed.
19 A process as claimed in claim 18, the filtrate such as zinc sulphate is either crystallized and sold as by-product or treated with lime to regenerate the ammonia gas to a storage vessel for reuse.

20 A process as claimed in claim 19, the manufacturing process is pollution free as nothing is discharged to the atmosphere nor any liquid is to be disposed. Only in case of regeneration of ammonia by lime, calcium sulphate will be formed which is harmless. There is no fuel to be burnt and hence no waste gases produced.
21 A process as claimed in claim 20, the manufacturing process is one of the cheapest as it can use any zinc containing raw material, irrespective of its impurities, where there is no limitation. There is no waste of the byproduct which is a valuable fertilizer. There is no involvement of high temperature and expensive fuel.
22 A process as claimed in claim 21, the process has excellent control on the qualify of the product, in respect to purity, grain size, brightness and bulk density and is equivalent or better than French process, white seal grade ,
23 A process as claimed in claim 22, the process is free from air and water pollution which is the greatest advantage in today's times, compared to any known process.
Dated this 5th day of MARCH 2007


The present invention relates to a process for converting metallic zinc, zinc dross, zinc ash and horn, zinc hydroxide, zinc ores or any other form of zinc in metallic or impure oxide form to zinc oxide by converting them to acid salt solutions, purifying them and passing Ammonia gas to directly precipitate out zinc oxide.








689-MUM-2007-CLAIMS(MARKED COPY)-(12-7-2012).pdf








689-mum-2007-description (complete).pdf

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689-mum-2007-form 2(title page)-(complete)-(5-4-2007).pdf

689-MUM-2007-FORM 3(18-6-2012).pdf

689-MUM-2007-FORM 5(18-6-2012).pdf





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689-MUM-2007-REPLY TO EXAMINATION REPORT(18-6-2012).pdf

Patent Number 256548
Indian Patent Application Number 689/MUM/2007
PG Journal Number 27/2013
Publication Date 05-Jul-2013
Grant Date 01-Jul-2013
Date of Filing 05-Apr-2007
Applicant Address 10/1, GEETA SOCIETY, CHARAI, THANE-400601
# Inventor's Name Inventor's Address
PCT International Classification Number C01B31/24
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA