Acidic Oxides - Company Case Study

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CASE STUDY 1: Xstrata
Produced Acidic Oxide – SULFUR DIOXIDE
Industrial Process –
Sulfur Dioxide is an acidic oxide produced domestically and industrially in many ways. Xstrata, particularly Mount Isa Mines LTD, produces sulfur dioxide as a by-product from the extraction of copper from ores.

Copper ore mined in Australia is predominantly chalcopyrite (CuFeS2), a sulfide ore of copper. The extraction of copper begins with crushing the ore and subjecting the crushed ore to froth floatation. In this the concentrated copper ores float to the top of a bath and are collected, and the gangue (rock and other unwanted silicate materials) are left behind. The concentrated ore is now predominantly CuFeS2 and is roasted in air with the following effects -

2CuFeS2(s) + 3O2 → 2CuS(s) + 2FeO(s) + 2SO2(g)
This is the first time sulfur dioxide is produced in the extraction process. The Copper (II) Sulfide (CuS) is then heated at 1100oC, with crushed limestone and sand, and is converted to Copper (I) Sulfide (Cu2S). The Copper (I) Sulfide is then roasted in air and some is oxidised to Cu2O. These two then react to form Copper metal, Both reactions described below –

2Cu2S(s) + 3O2(g) → 2Cu2O + 2SO2
2Cu2O(s) + Cu2S(s) → 6Cu(l) +SO2
This is the end of the processes that produce the oxide. The Copper goes through more refining electrolytically. Evidently, Sulfur Dioxide is a major by-product Impacts –
Sulfur Dioxide (SO2) has many detrimental effects to society and environment. Firstly, exposure to high levels (10-50 parts per million (PPM)) of SO2 can cause irritation to the eyes, throat, nose and airways. This causing coughing, wheezing and serious breathing problems to asthma sufferers. A more common effect on society and the environment is it dissolving in water and oxygen in the atmosphere to form acid rain –

SO2(g) + H2O(g) → H2SO3
2H2SO3 + O2 → 2H2SO4
Sulfuric Acid (H2SO4) is a result of the reaction in the is the main component of acid rain which has many negative effects. It accelerates the decay of man-made structures such as buildings and statues, making them unattractive and in need of repair, which society has to pay for, through the government or businesses. For example concrete, limestone and marble (both of which have are made of calcium carbonate) and metal structures –

Ca(OH)2 + H2SO4 → CaSO4 + 2H2O
CaCO3 + H2SO4 → CaSO4(aq) + H2O + CO2
Fe(s) + H2SO4 → FeSO4(aq) + H2
As above, acid rain turns an ingredient of concrete into a much weaker salt; and limestone/marble and metal into an aqueous solution, which will get washed away in water. Over the years can lead to little structural integrity and the accelerated erosion of statues, pillars and other monuments.

It also effects the environment through altering forests, lakes and and aquatic habitats. Plants' leaves and stems are harmed as well as the soil being contaminated, leading to insufficient nutrients to the roots of plants which may lead to the plant not being able to photosynthesise or reproduce. This has many roll on effects being lose of habitat of animals in forest and change in the hydro-environment. With the acidity of water increasing comes with disturbances with chemical equilibriums of fish and eggs. This causes disturbances with their life and waste cycle – which is detrimental to their species. Company Steps to Minimise Release –

Mount Isa Mine LTD, has taken many steps to try and minimise the release of this Sulfur Dioxide. The most significant step being the introduction of an acid plant in 2000. The acid plant collects the majority of the Sulfur Dioxide emissions from the smelter, turns them to sulfuric acid and transport this to other plants for use in the production of fertilisers –

2SO2 + O2 -----> 3SO3
SO3 + H2SO4 → H2S2O7
H2S2O7 + H2O → H2SO4
The plant has decreased the Sulfur Dioxide emissions by 76% since it's establishment.
In conjunction with the plant, the company installed a wet scrubber...
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