Zinc

Source : http://www.miningplazza.com.au/mining-information/130-zinc.html

Introduction

 

Produced jointly by the Minerals Council of Australia and AGSO

Zinc (Zn) was used in Rome and China more than 2000 years ago as a component of brass (zinc-copper alloy). Zinc metal was first smelted from zinc ore in India in about 1200 and is known to have been used in China soon after. Commercial production of zinc did not start in Europe until the middle of the 18th century and in the United States until 1860. In deposits mined today, zinc ore (rock containing economic content of zinc and/or other materials) usually occurs mixed with ores of lead, silver and commonly copper, and is extracted as a co-product of these metals.

Zinc is used for galvanising (coating) iron and steel to protect against rust in large-scale construction projects, in motor vehicle bodies and roof sheeting.

Occurrence

The main zinc mineral is sphalerite (Zn,FeS), which contains up to 67% zinc. Smithsonite (ZnCO3, 52% zinc), willemite (Zn2SiO4, 59% zinc) and hemimorphite (Zn4Si2O7(OH)2 H2O, 54% zinc) may occur in the near-surface weathered or oxidised zone of an orebody.

Deposits containing zinc form from hot (hydrothermal) fluids generated within the earth. These fluids may be trapped below the surface in cracks where sphalerite and other minerals may precipitate to make vein deposits. Where limestones occur, the fluids may fill cavities to form rich but patchy deposits. Some fluids may reach the ocean floor in areas of underwater volcanic activity to form 'volcanogenic' deposits. Some are forming today under the ocean off Papua New Guinea and Canada. Other fluids may escape to the surface through cracks or faults into small shallow lakes or seas and, if conditions are right, lead-zinc-silver deposits may form.

For thousands of millions of years, deposits have been forming in this manner and may eventually be exposed at the surface following weathering and erosion. Some are completely eroded away and may be recycled by natural processes into new deposits. Partially eroded deposits were relatively easy to discover, examples are the Broken Hill and Mt Isa deposits, found late last and early this century. These deposits formed the basis of Australia's zinc mining industry.

Exposed deposits are becoming harder to find in Australia and exploration companies are now looking beneath the surface for the deposits of the future. This is a more costly and difficult way to find orebodies but a series of successes have occurred since the late 1970s. Such discoveries include the Scuddles mine (140 metres deep) and Admiral Bay (1.5 kilometres deep) in Western Australia, the Cannington deposit (10 metres deep) in north Queensland, the Hellyer mine (90 metres deep) in Tasmania and the Wilga deposit (50 metres deep) in Victoria.

Australian resources and deposits

In 1883, Charles Rasp discovered the rich, large Broken Hill lead-zinc-silver deposit in New South Wales (NSW) deposit when he found some dark, heavy rocks which he thought may contain tin. Subsequent assays (analyses) of these rocks proved that he had located rich oxidised (weathered) silver and lead minerals. Broken Hill provided the basis for Australia's current major zinc mining industry . Over 100 years later ore is still being mined at Broken Hill and it has been the largest producer of lead-zinc-silver in Australia.

The rich lodes at Mt Isa were not discovered until 1923 and were developed despite the remote location and harsh environment. The nearby, rich Hilton deposit was discovered in the late 1940s but not developed until the mid-1980s. Production at Mt Isa continues and it has been the second biggest zinc producer in Australia. In the Mt Isa region, there are large mines at the George Fisher, Cannington and Century deposits, while the Dugald River and Lady Loretta deposits are yet to be developed. In the Northern Territory, the large McArthur River deposit is a major producer.

Zinc ore is also produced at Rosebery and Hellyer in Tasmania; Elura in NSW; and Pillara, Goongewa, Scuddles and Gossan Hill in WA . High-grade zinc silicate ore is mined intermittently from the small Beltana deposit in South Australia.

Australia in the world

Australia ranks first in the world in economic zinc resources because of the development of the large, world-class zinc-lead-silver deposits at McArthur River, Cannington and Century. This position is further supported by resources in the many other deposits of various sizes in Australia.

Australia ranks third behind China and Canada in world mine production and second to Canada in exports of zinc. Australia exports zinc as refined metal to a broad range of destinations in the Asia Pacific area, from India to the USA, but mainly to Indonesia, Hong Kong, Chinese Taipei and Malaysia. Our major customers for zinc in ores and concentrates are Japan and South Korea, and to a lesser extent Belgium, Germany and the United Kingdom.

Australia is also at the forefront of technological development in zinc mining and processing.

Mining and processing

In the early days of Broken Hill, zinc ore was rejected to the waste dumps because virtually none of the zinc could be extracted economically. Gravity and magnetic separation methods were unsuccessful. In 1901 a flotation process was devised at Broken Hill which achieved recovery of upwards of 60% of the zinc minerals from ore. After considerable experimentation, a selective flotation method that worked on a commercial scale was perfected in 1912. Improved versions of this flotation process, such as the Australian-developed Jameson flotation cell, are used world-wide today. The Jameson flotation cell is installed in many mines around Australia.

Almost all of Australia's zinc mines are underground operations and are highly mechanised. Ore is drilled and blasted in large volumes, transferred to underground rock crushers by large loaders and trucks, and then hoisted to the surface in skips or driven directly to the surface by truck via a spiral access tunnel (decline). Century is Australia's only large surface open pit zinc mine (so hoisting is not required), where ore extraction is by similar methods.

At the surface, the ore is subjected to additional crushing and fine grinding. The flotation process is then used to separate the zinc and other valuable sulphide minerals from the waste rock particles (tailings) to form a concentrate.

Ground ore, water and special chemicals are mixed and constantly agitated in banks of flotation cells. Air is blown through the mixture in each cell, and the fine zinc sulphide particles stick to the bubbles, which rise to form a froth on the surface of the flotation cell. The tailings sink and are removed from the bottom of the cell. The froth is skimmed off and the resulting zinc sulphide concentrate is dried. This process upgrades the ore, which may contain only 6% Zn, to a concentrate assaying more than 50% zinc. Up to 90% of the zinc in the ore can be recovered.

Electrolysis and smelting are the two processes used to produce zinc metal in Australia. The electrolytic process is used at the Risdon zinc refinery in Tasmania, where zinc concentrate from various Australian mines is roasted to eliminate most of the sulphur, as sulphur dioxide, and make impure zinc oxide. The roasted concentrate is then leached with sulphuric acid to form zinc sulphate solution. The zinc sulphate solution is purified by adding a small amount of zinc powder to precipitate and remove traces of copper, cadmium, cobalt and nickel. The solution is piped to electrolytic cells, where the zinc is electrochemically deposited on aluminium cathodes (electrodes). The zinc is removed from the cathodes, melted in a furnace and cast into slabs.

The smelting process is used at Cockle Creek near Newcastle in NSW, to produce zinc (and lead) metal simultaneously in a blast furnace. Zinc and lead concentrates from various mines are blended and sintered (partly melted) to combine the fine particles into lumps and remove some sulphur as sulphur dioxide. The sintered product is mixed with coke and smelted in a blast furnace to produce zinc vapour (gas), which is condensed by cooling with a spray of molten lead to form impure molten zinc metal (98.3% Zn). To remove the small amount of lead and cadmium impurities the liquid zinc is twice boiled to zinc vapour and recondensed to produce high purity zinc metal (up to 99.95% Zn).

At Port Pirie, zinc is recovered from the lead smelter slag (molten waste), which contains about 17% zinc, and residues from the Risdon zinc refinery in Tasmania. The molten slag is heated further to drive off zinc (and some lead) vapour, which is oxidised to form a zinc oxide fume and filtered out as dust in a 'bag filter'. This dust is ground and put through an electrolytic refining plant to produce high purity zinc.

Primary refined zinc is produced at three plants - Risdon (Tasmania), Cockle Creek (NSW), and Port Pirie (SA), while production at the new Townsville zinc refinery is expected in late 1999. Small production of secondary refined zinc occurs at Port Kembla (NSW). Zinc oxide and zinc dust is produced from primary and scrap zinc at West Footscray in Melbourne (Victoria) and in minor amounts in Brisbane (Queensland).

Risdon is Australia's largest zinc refinery and also one of the largest in the world. Overall zinc recovery from concentrates is about 95%. Less than half of Australia's zinc concentrates are processed domestically.

Uses

A large part of the world's zinc is used as protective galvanised coatings for iron and steel. In Australia, this use accounts for well over half of the domestic sales of zinc. The widespread use of zinc as a protective coating is mainly because of its resistance to normal weathering, and the protection given to steel by the preferential corrosion of zinc when the underlying iron or steel is exposed. This is an electro-chemical reaction known as galvanic action. The construction and appliance manufacturing industries use large amounts of zinc, mainly as coatings on steel beams, sheet steel and vehicle panels in the automotive industry.

Zinc is also used in alloy die cast products, zinc pigments, zinc salts, zinc oxide as additives to rubber and for zinc chemicals in agriculture, and for wrought or rolled zinc products.

Suggestions for further reading

Blainey, G 1993 The Rush that Never Ended: A History Of Australian Mining, 4th edition, Melbourne University Press, Melbourne.

Australian Geological Survey Organisation 1999 Australia's Identified Mineral Resources 1999, Australian Geological Survey Organisation, Canberra.

Hughes, F.E.(Ed) 1990 Geology of the Mineral Deposits of Australia and Papua New Guinea, Australasian Institute of Mining and Metallurgy, Monograph 14.

Roarty, M.J. 1989 Zinc In Australian Mineral Industry Annual Review for 1987, A. Paine (Ed) Australian Government Publishing Service, Canberra, pp266-275.

Woodcock, J.T. and Hamilton, J.K. (Eds) 1993 Australasian Mining and Metallurgy: The Sir Maurice Mawby Memorial Volume. Australasian Institute of Mining and Metallurgy, Monograph 19.

Kampung boy no more..Interview with Tun Che Det

Tagged by Kak Milah on her notes in Facebook on Sunday, 31/01/10

Sunday January 31, 2010

Access to information equals opportunities. With the Internet today, such access is almost limitless but only those who seize the opportunities will get ahead, says Tun Dr Mahathir Mohamad.

IN a recent interview with Open University Malaysia (OUM), former Prime Minister Tun Dr Mahathir Mohamad shares his views on the challenges that educational institutions face and the direction they should take. He adds that immigration policies should be reviewed, as they stop the brains from coming in, but allow the uneducated to work here instead.

Below are excerpts from the interview.


Dr Mahathir believes that a lifelong learning habit begins with a love for reading.
Q: In some countries, going back to school is regarded as the norm. What are Tun’s views on lifelong learning? What does it take to encourage more Malaysians to participate in lifelong learning?

A: We gain knowledge through many sources, among which is, of course, reading. To participate in lifelong learning, one must first love learning and to love learning, one must first love reading.

Of course, we can also acquire knowledge through television but we cannot gain an education just by watching television alone. They say a picture paints a thousand words. Sometimes when you look at a picture, you see not just one but many thousands of words. However, understanding still may not come and so you do not produce.

Reading is different. It stays in your mind longer. You learn when you read. You learn not only the knowledge contained in the book but also the language, the way the book is written.

So, reading improves communication. A person who watches television cannot learn to communicate; a person who reads books can. And communication is one of the weaknesses in human society. The ability to convey your thinking to another person is a communication skill.

Through reading, the process of lifelong learning begins. Once you start reading, you cannot stop reading. Of course, the person who starts watching television also may not be able to stop watching it, but what he learns from television may not be good for him. But when he reads, even if it is only a story book, he will, at least, acquire the skill of communication.

Reading also improves your perception of things and trains you to analyse and understand complex matters. The more you read, the more you acquire the experience of others albeit through the eyes of a skilful observer. Even if you are reading a story book, your ability to solve problems increases because you have, at least, read about it.

I started reading when I was young. Books tell me what people will do in 10 years’ time, they tell me how people think, they predict trends… If you don’t read, you will be left behind.

To encourage lifelong learning, you must instil a reading culture. Lifelong learning starts with reading, and can become a habit, just like reading.

Q: The world is increasingly becoming a global village and more of our young people are working overseas. How can we turn this increased mobility of youth and talent to our nation’s advantage?

A: Globalisation is the trend today. But it aggravates the brain drain in Malaysia. To understand this, we need to look at our immigration policies, which were formulated in the 1950s when people could not travel easily.

We did not want people coming into the country then, so our policies stopped people coming in. We believed our people would not want to go out, so our policies did not stop them going out.

But today, the world has changed. It is now very easy to travel; it only takes about 20 hours to fly to the other side of the world. With this ease in travel, physical borders can no longer stop people from entering or leaving a country. So people go out, especially those with knowledge and skills. Other countries offer them high wages and we do not stop them, so they leave and we lose our best people.

At the same time, we have a policy which actually stops brains from coming in. But we also need workers, so we allow uneducated people to come in.

So, what we get is no inflow of brain but inflow of the brainless.

All this is because we are using an outdated immigration policy. We must remember that in future, all countries will have a multi-racial population. There won’t be a single-ethnic nation anymore. Five million of the people in France today are Algerians. England has many Indian restaurants. People will be moving around, either legally or illegally, and settling down where they like.

The only country that may not change is China, with its 1.3 billion people. People who go to China become Chinese. Kublai Khan conquered China and became Chinese. The Manchus conquered China and became Chinese. There are so many Chinese; you get diluted, the Chinese don’t.

To attract youth and talent, we need to change our policy to consider the mobility of youth and talent.

Q: What is the greatest challenge that higher education faces in the next decade? What opportunities should we look out for?

A: You cannot recognise challenges and opportunities unless you understand what is happening around you. That is where learning comes in — learning helps you to comprehend, analyse and tackle problems.

Globalisation is clearly a challenge. With globalisation, your knowledge widens and you learn to deal with things you may not otherwise be able to.

Take a person born in the kampung, for example. His knowledge of things is limited to what he sees there. Once he moves to the city, he sees and learns so much more. Everywhere in the world, people in rural areas are regarded as less capable, less savvy, less sophisticated. But with globalisation, the kampung boy can cross new frontiers, embrace new values, see new ways of doing things. Globalisation gives the kampung boy a new world to comprehend, new skills to develop, new relationships to handle. Those are tremendous challenges.

Opportunities are different. Opportunities are affected by our ability to access and classify information. In the past, when we did not have much access to information, our opportunities were limited. Today, with the Internet, we have access to information and plenty of facts, but we need to know how to classify and use these facts.

So today, we have the capacity but the problem is, how do we use this capacity? The people who are able to use this capacity will see the opportunities – Google, Yahoo... In the end, seeing opportunities and seizing them, it is all up to you.

Q: Technology is said to have liberalised and democratised education and we must compete on a global platform. How successful have our local public universities been in this respect?

A: Well, they are not too bad, but they are not too good either. University authorities need to reassess their roles. It’s not just a question of giving sufficient knowledge to students so that they can pass their exams.

Knowledge must be viewed in a wider context. In the hands of some people, knowledge can bring about harm. What I notice about our public universities is that not enough attention is given to human character development and nurturing value systems which can help students become useful people in society.

Without the right values, knowledge can even make someone a criminal. But if you are shaped by the education system to become someone useful in society, then education would have fulfilled the greater need. There is a need for universities to strike a balance between producing skilled knowledge workers and people with good moral values.

Q: What is Tun’s perception of world university rankings and the role of universities?

A: Our universities today are much more aware that they are not just institutions for imparting knowledge but also institutions for researching new knowledge. Unfortunately, some still don’t have that mindset. Universities need to understand that their function is not just to transfer knowledge but also to create new knowledge through research, and to write about it, through producing papers. That is a crucial role.

Rankings should be based on the type of universities. Of course, you cannot compare an open university with conventional universities. You will get different results because the criteria are not the same. That, I think, is not important. What is important for an open university is whether it can provide education for people who have missed the boat, and for as many people as possible without compromising on quality.

When I was a small boy, my teacher only passed Standard Four. Later, a teacher had to have secondary school qualifications. Today, even that is not enough. Entry qualifications keep getting higher. Later, we will need more people with doctorates. The progress of society is such that, over time, the level of knowledge increases. So there is always a need to upgrade skills and qualifications, and OUM has a clear role to play.

Q: What is your secret for staying so young?

A: Oh, I do my usual physical exercises and I enjoy horse riding. But I also read. It is something I have enjoyed since young. My father was very strict about reading. Everyday, when he got home from work, he would cough in front of the house and I’d rush to get a book to read so as not to get scolded. Besides, I can do other things when I am reading. That is good because I don’t like to waste time (smiles).

■ By OUM president and vice-chancellor Prof Emeritus Tan Sri Anuwar Ali, senior vice-president Prof Mansor Fadzil and senior lecturer Dr Janet Woo Tai Kwan. For full interview, see
http://www2.oum.edu.my/v2/eoumtoday/2010/jan-issue66-2010/