Extraction Of Iron

Iron, perhaps the most important element to all civilization is also one of earth's most abundant. Like the majority of metal ores, iron ores are not pure compounds. Rather, most iron ore are polluted with sand, rock and silica.

The process of extracting iron involves a number of steps.

The first step to concentrate the iron ore and remove its contents of

To further remove any existing impurities, a complex process takes place in a . The is where materials are placed into the blast furnace. These materials are: Ore, Limestone and Coke.

A burst of hot, oxygen enriched air is blown into thelocated at the near bottom of the furnace. What follows are a number of and type reactions which ultimately produce the metallic iron.

One of these reactions is the coke being burnt. The heat generated by this reaction increases the bottom of the furnace to a temperature near 19000° C. This reaction is represented in a chemical equation:

C(s) + O2(g) ® CO2(g) + heat

The generated rises halfway up the furnace, where it reacts with the hotter coke. This causes the carbon dioxide to reduce into . This reaction absorbs some heat and lowers the temperature of the upper part of the furnace to roughly 1300° C.

CO2(g) + C(s) + heat ® 2CO(g)

This carbon monoxide then reduces the iron oxide to a metallic iron, which is at the temperature of the reaction. This takes place in middle and upper parts of the furnace.

3CO(g) + Fe2O3(s) ® 2Fe(l) + 3CO2(g)

The in the charge is ...

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C(s) + O2(g) ® CO2(g) + heat

CO2(g) + C(s) + heat ® 2CO(g)

This carbon monoxide then reduces the iron oxide to a metallic iron, which is at the temperature of the reaction. This takes place in middle and upper parts of the furnace.

3CO(g) + Fe2O3(s) ® 2Fe(l) + 3CO2(g)

The in the charge is to remove any existing silica left in the enriched ore. There are two steps in this process.

The first step is heating the limestone in the furnace to produce , CaO. This takes place in the middle of the furnace.

CaCO3(s) ® CaO(s) + CO2(g)

The second step in this process is when the lime reacts with the silica, resulting in.

CaO(s) ® SiO2(s) + CaSiO2(l)

At this point, the calcium silicate is a liquid which seems to mean that the lime has served as a . The term flux refers to a substance that cause mineral impurities in an ore to melt more readily. The melting process that takes place in the furnace is called . In this process of smelting, the products in the furnace are separated into layers. In this way, the molten iron is the bottom layer and molten calcium silicate is the layer above it. Being that the molten iron is more dense than the molten calcium silicate.

The calcium silicate is a kind of , formed in a smelting process by the lime combining with the calcium silicate. As a slag, the calcium is easily separated from the more dense molten iron. This is done simply by tapping the slag with an outlet.

When cooled, the molten iron from the blast furnace becomes . It still contains a number of impurities; Sulfur, Phosphorus and Boron.

These lower the iron's tensile strength and make it more brittle. However, it has such impurities at much lower levels.

Gold Extraction

Gold occurs as a free element in the earth, usually in nugget shapes. Gold is recovered by the carbon in pulp process after first concentrating the ore. The major steps in the extraction of gold metal from its ore is as follows:

Host rocks and specs of gold

Froth flotation

Concentrated Gold Ore

Cyanide process

Au(CN)2 – (aq)

Add zinc or electrolysis

Au(s)

The gold present in the concentrated and finely crushed ore is leached out by an alkaline solution of sodium cyanide. Oxygen acts as the oxidizing agent with the assistance of the cyanide ion. Gold has been used in jewelry for its colour and its inert nature. Gold is at the bottom of the reactivity and this makes it easy to extract. Gold does not corrode because it doesn’t react with much at all.

Oxidation: Au(s) + 2CN-(aq) → (Au(CN)2)-(aq) + e-

Reduction: O2(g) +2H2O(l) +4e- → 4OH-(aq)

4Au(s) + 8CN-(aq) + 2H2O(l) +O2(g) → 4Au(CN)2-(aq) +4OH-(aq)

The Au(CN)2-(aq) is separated from the pulp using activated carbon. The gold is then recovered by adding Zinc (metal ion displacement) or by electrolysis.

The dissolved Au(CN)2- is separated from the pulp by adsorption on activated carbon in adsorption tanks. The activated carbon is made from vegetable matter such as fruit pips, coconut husks or peat by heating to about 900deg C in the presence of steam and the absence of air.

Some ores require additional processing before being treated using the CIP process. This treatment may involve flotation, which serves to concentrate the ore, and roasting, which destroys the mineral structure and makes the gold more accessible to leaching by cyanide. The remaining concentrate can then be successfully treated using the carbon-in-pulp process.

Peer Reviews

Here's what a star student thought of this essay

cheekymokeyxxx

10th of Feb 2012

Quality of writing

The technical terms used are to the level expected at GCSE and in some cases go beyond this level. The student has followed scientific conventions and rules about writing about process by not dramatising or adding in information that is not relevant. The spelling, punctuatuon and grammar are all fine. Just remember that explain terms and phrases that you would not have understood before you went on the course to show your teacher/the examiner what you have learnt as this will help you gain extra marks.

Level of analysis

The fact that equations and diagrams that are relevant and explained not just put in for the sake of shows that the student knows what they are talking about. But some words I do believe could have been explained to a greater extent because it left me wondering if tne student did at some points know what they were talking about. Otherwise this is a well planned and thought out response. The fact that background information has been given on the two metals gives the reader a context in which to place the two extraction processes. Underlining key phrases and terms is a scientific skill that will help you pick up marks easier as the examiner will not have go hunting for the marking points they will be immediately brought to his attention.