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9.4 Caring for the country 7. Rehabilitation of contaminated sites

Syllabus reference (October 2002 version)
7. Rehabilitation and safe use of previously contaminated sites	Students learn to: define the qualities of geological features that need to be considered in selecting areas for waste dumps evaluate the methods currently used for the disposal, treatment and recycling of both solid and liquid waste assess the methods and effectiveness of rehabilitation at a contaminated mine site	Students: perform investigations to construct and test simulations of waste treatment processes, such as filtration, sedimentation and precipitation gather information from first-hand investigations or secondary information to analyse the effectiveness of landfills in disposing of solid and liquid wastes

Extract from Earth and Environmental Science Stage 6 Syllabus (Amended October 2002). © Board of Studies, NSW

Prior learning: Preliminary module 8.5.3, HSC Module 9.2 (subsections 2 & 4)

Background Information: In the 19^th and early 20^th centuries mines were not regulated in Australia and abandoned mines were not rehabilitated and were hazardous. Today the government keeps a bond so that if a mining company does not comply with the rehabilitation regulations, the bond money can be used. Most companies today want to protect their reputation and some companies do even more than is required by law. However, there is a backlog of old mines that have to be rehabilitated and the companies often no longer exist, so the government has to rehabilitate the mines at public expense.

perform investigations to construct and test simulations of waste treatment processes, such as filtration, sedimentation and precipitation

To plan your activity you will need to consider the equipment that the school has and what waste material you will use. Below are two procedures that you could adapt. You will need to consider safety factors and not handle waste material that is toxic or hazardous. Will you be treating soluble or insoluble material? Will you use the four methods listed above or include a different method? If you live in a mining area, talk to people at the local mine and find out what waste material is produced during mining and during the processing of the raw material.
Choose the best equipment for the treatment processes you are doing. Talk to the teacher and think about how you are going to set up the equipment. You may choose to have a different group doing each method, then reporting back to the rest of the class. Filtration will be fairly straightforward but you will need to revise how to use the equipment if you haven't used it recently. If you do sedimentation, you will need to allow plenty of time for the particles to settle out.
When you are ready to start the investigation, perform it carefully so you will have a successful separation. If your technique is difficult, you may plan to do it several times and note what you collect each time. Either average your results or reject your first results and average the rest. Why is it a good idea to repeat the experiment several times and average the results?

Procedures to simulate waste treatment processes

Aeration simulation

Froth flotation is a technique that employs the principles of aeration and is used in the mining industry to separate ore minerals from crushed rock.

To simulate the technique you need to follow the procedure below:

Mix iron filings with the sand and place this mixture in a 500 mL jar. Ensure that the depth of the mixture in the jar is no more than 1 cm.
Fill the jar half full with water.
Mix the water in with the sand and iron mixture. If your jar has a lid, place the lid on and shake the mixture.
Add 2 cm of kerosene to the jar. Avoid any skin or eye contact with the kerosene. If kerosene comes into contact with your skin or eyes, wash thoroughly with water.
Add the equivalent of an eye-dropper full of detergent.
Using a straw, blow bubbles into the mixture. If you don't have a straw, you can create bubbles by placing the lid on the jar and shaking the jar. Look for the iron filings sticking to the air bubbles that are being brought to the surface.

Precipitation

Precipitation reactions are used to separate metals what are dissolved in waste concentrate. This activity demonstrates how a precipitate can form when two solutions react.

What you need:

Epsom salt (magnesium sulfate, MgSO₄), which you can purchase from a nursery.
Washing soda (sodium carbonate, Na₂CO₃), which is found in the powdered detergents section of supermarkets.
Three glass jars, labels removed.

Procedure:

Make a solution of Epsom salts in one jar. Add one level teaspoon of Epsom salts to about 25 mL of water.
Make a solution of washing soda in another jar. Again, add one level teaspoon of washing soda to about 25 mL of water.
Pour each solution into the third jar and record your observations in the table below.
Let this solution stand over night and then record your observations the next day in the table below.

You should observe a white milky precipitate of magnesium carbonate. The chemical formula for this reaction is:

MgSO₄ + Na₂CO₃ MgCO₃ + Na₂SO₄

Sodium sulfate (Na₂SO₄), also produced, remains in solution while the magnesium carbonate (MgCO₃) should settle out as the precipitate.

define the qualities of geological features that need to be considered in selecting areas for waste dumps

Some features that should be considered are:

Soil and rock type: the rock needs to have low porosity and low permeability so that the wastes will not leach into water or will not permeate down to other rocks and then eventually into groundwater. There should be little or no faulting and fracturing of rock.
Potential for landslides: a landslide would expose the waste material and could enable toxic gases to escape into the atmosphere.
Earthquake activity: an earthquake could fracture what were stable rocks and release the wastes into another area, such as groundwater.
Lack of groundwater: if groundwater is present the waste material could be carried many kilometres away and could contaminate pristine soil and eventually end up in an aquifer that is the water source for animals or people.
Orientations of structures such as bedding and foliation. If the rock has been tilted, it is more likely that the material would seep between the bedding layers and end up in groundwater below the rock.

gather information from first-hand investigations or secondary information to analyse the effectiveness of landfills in disposing of solid and liquid wastes

To do a first hand investigation, it may be best to visit a landfill site. Talk to the EPA or the local council to see if they are aware of a landfill site in your area. You could investigate the Olympic site and obtain information about how the Olympic Co-ordinating Authority rehabilitated the section that was originally a landfill site.

In addition you could conduct a simulation. You could use plastic as an impermeable material to stop leaching of dangerous material into the watertable. Alternatively you could use a large piece of rock, like sandstone. You could put soil above the material and put your waste material in the soil. You can't use dangerous materials for safety reasons but you could use some waste oil or solid material, such as metal, wood, concrete, plastic or other materials like that. You might choose to use organic material, such as food scraps. A procedure that uses food scraps is provided below. Evaluate the shortcomings of your simulation. Consider for instance that wastes in a real landfill site may be there for tens of years before any problems arise.

An engineered landfill simulation

This is a simple activity designed to show how decomposing waste can be used to generate natural gas.

What you will need:

a plastic soft drink bottle, about 1 to 2 litres in capacity
organic waste material, such as food waste
a sharp object, such as a skewer
matches and candle.

What to do:

Fill about one quarter of the bottle with organic waste, such as banana peels, ends of tomatoes, bread crusts, apple cores and the like.
Squeeze the bottle inwards and then place the lid on tightly.
Place the bottle in a warm spot, for example, on a window-sill in the sun.
Observe what happens to the waste materials and the bottle over three weeks. Record your observations.
After three weeks, puncture a small hole through the lid by using the sharp implement. Take care no to cut yourself. You may wish to get a friend to help you.

As soon as you have made a hole in the lid of the bottle, hold a lit match at the hole to see if it lights like a candle. Do not look directly over the top of the bottle.

Should you wish to gather secondary information the following sites may be useful.

Environment Protection Authority's web site This will take you to Environmental Guidelines: Assessment, Classification and Management of liquid and Non-liquid Wastes document. Click on Environmental Guidelines: Assessment, Classification and Management of liquid and Non-liquid Wastes PDF. When the document opens go to Section 4 Managing Classified Waste and look at 4.4, 4.5, 4.6 and 4.8.The EPA has other documents that are not available on the Internet but you can obtain them by ringing 13 1555 for the cost of a local call from outside the Sydney region.
An example of landfill in a county in the US El Dorado County, California, USA.

evaluate the methods currently used for the disposal, treatment and recycling of both solid and liquid waste

Some methods currently applied to solid waste include the following:

Landfill

Around 97% of all solid industrial, commercial and domestic waste is disposed of as landfill in NSW.

At Lucas Heights, two organisations ( Waste Service NSW and the Cooperative Research Centre for Waste Management and Pollution Control Ltd.) have engineered a special type of landfill, referred to as a bioreactor, which encourages waste to breakdown and decay.

Accepted practice in the management of landfills has been to limit the amount of ground water running through the waste material as this water has the potential to become contaminated. In a bioreactor, water that has passed through the waste material is collected and then fed back through the waste once again. This bacteria-rich water actually helps the waste to breakdown even faster. Natural breakdown of waste material has been reduce from decades to years. Another advantage of the system is an increase production of methane, which can then be used to generate electricity. 1 million tonnes of waste provides enough electricity for 1000 average homes for a year.

Recycling and reuse

Increasingly, waste sites are incorporating reuse areas where people can leave unwanted or damaged household items. These items can be recovered by people who may have a use for them rather than the item being destroyed or taking up valuable space in landfill.

Recycling and reprocessing

This is an alternative for those solid materials that have value to the community and is preferred to discarding to landfill. Following are descriptions and evaluations of some examples.

Glass

There is no limit to the number of times that most glass products can by recycled. In Australia 43% of our glass is recycled. New glass can be made with up to 100% waste glass. Some glass products have special qualities and uses that make them non-recyclable. These must be taken out before the glass is crushed into cullet. Non-recyclable glass included mirrors, window glass, crystal, ceramics, ovenproof materials, medical and laboratory glass as well as light bulbs.

Paper

Paper can be recycled into a wide range of products. However contamination problems limit its reuse in food packaging. The degradation in fibres during recycling results in the downgrading of the recycled paper.

As a result, old newspapers cannot be used to produce high quality printing and writing papers. However, they can be used to produce newsprint (the paper used to make newspaper) and tissue paper.

The degradation of fibre during recycling also limits the number of times that a paper fibre can be recycled. Adding some new fibre or good quality waste fibres to the recycled pulp can improve the quality of the recycled product.

Unlike the process of making paper from new raw materials, making paper from waste paper rarely requires chemical pre-treatment. The waste paper is mixed with water in a machine that looks like a giant blender and is converted into a thin slurry of individual fibres. This slurry is treated to remove contaminants, such as plastic, string and paper clips, using sophisticated screening techniques. The slurry then continues on and passes over a continuously vibrating mesh. The water in the pulp drains through the mesh leaving the fibres behind on the mesh. This damp paper is then passed over a series of rollers to flatten and dry it.

In some cases starch is added to the surface of the paper to give it the required characteristics. At the end of the process, the paper is then rolled onto large spools and sent to factories where it is cut to size and shape.

Although old newspapers have been used for many years to make packaging materials, until recently they were not used to make recycled newsprint due to the difficulties with the de-inking process. These difficulties have said to been resolved and a new de-inking and recycling plant in Albury NSW is now producing newsprint using a mixture of old newspaper and magazines with new raw products. All newsprint manufactured in Australia now contains up to 40% recycled fibre.

Old newspapers are also recycled into other products such as cardboard, packaging, housing insulation and animal bedding.

A range of methods have been applied to liquid waste, such as paints, dyes, glues, wash water from the cleaning of contaminated tanks, acids, alkalis, oil, oil based sludges, solvents and some organic chemicals.

Up until about 1974, about 70% of all industrial liquid wastes were deposited in local council tips. The rest were probably deposited illegally in bushland, local creeks or down stormwater systems and sewers.

Since 1974, Waste Management centres have been developing new and innovative ways to treat liquid waste. Following is a procedure that outlines one of the most recent.

A current method in treating liquid waste

Liquid wastes are picked up from industrial sites by specially designed tanker trucks. When the tanker arrives at the liquid waste plant, the waste is sampled and analysed. The waste is then deposited through screens to remove any large solids and into the appropriate storage tanks, as determined from the initial sampling.

When the storage tank is full, it is once again sampled and analysed to determine what chemicals need to be added to the waste to begin the treatment process.

Polyelectrolytes are added that speed up the separation of the wastes as they are pumped into decanter centrifuges. The centrifuges spin the waste at high speeds and separate it into a lighter liquid, mainly water with traces of oil and some solids, and a heavier oily sludge. The oily sludge sticks to the outside of the centrifuge and is pumped to the fuel recovery plant, while the watery material is drawn off through the centre.

The watery liquid drawn off from the centrifuge is called the centrate, and flows through to an acidification reactor, which reduces its pH to between 3 and 5 so as to break down an oily emulsions.

A process called dissolved air flotation or froth flotation separates oils and any remaining solids. This process requires particular chemicals and air to be added to the mix, which allows these oily particles to rise to the surface on air bubbles. Once this occurs, they can then be skimmed off and sent to the fuel recovery plant.

The clear liquid left behind from the dissolved air are flotation is acidic, with some soluble organic material and heavy metals, such as iron and zinc, dissolved in solution. These metals are extracted through precipitation.

To precipitate out these metals from the solution, the pH is raised to between 8.5 and 9.0 by adding lime (calcium oxide). As a result, the metals precipitate out as solid hydroxides that then settle at the bottom of the tank.

This residue is then removed by settling the solids in a thickener. The water is drawn off from the top and the remaining material that has settled at the bottom is passed through a filterpress under high pressure to remove the remaining water.

The compressed hydroxide, called filtercake, is transported via a conveyor belt to a silo where it is stored prior to being deposited in a landfill site.

The water that is left behind still has a high organic content. Micro-organisms and warm air are added to the water, in what is known as an activated sludge facility, to break down this organic matter into carbon dioxide and water.

The oily sludge pumped from the centrifuge to the fuel recovery plant is dried in a heat exchange after being heated to 300^OC. Any water or low boiling point solvents are evaporated off from the sludge.

The toxic vapours produced are collected after condensing. The dried sludge is then referred to as recovered residue, and is disposed of in a landfill.

Current procedures for the treatment of liquid waste are effective, with benefits achieved at a number of stages.

Any oil present in the waste is not lost, but is removed to be used as a fuel. Heavy metals are also recovered. Water is separated and treated to a safe level, pure enough to flow out to the sea through the existing sewerage.

The toxic vapours produced are not allowed to escape into the atmosphere. Instead they are collected after condensing and then separated further into water and solvents. These solvents make good fuel and are reused to produce heat for the heat exchanges.

assess the methods and effectiveness of rehabilitation at a contaminated mine site

Rehabilitation leads to the restoration of the site to as near as possible to the original condition or better. Sometimes it is converted into recreation or residential areas.
Rehabilitation involves filling in mineshafts or excavation holes, putting back the topsoil while keeping the original contours of the land, and revegetating with the right mixture of plant species. It can also include indigenous animals being released into the area.
As ecological knowledge has increased, the complexity of the rehabilitation has also increased.

NOTE: It would be a good idea to study a specific mine for this syllabus point. Choose a mine that has been closed by checking with the Department of Mineral Resources. Research how the land was rehabilitated and assess if the rehabilitation was done satisfactorily. Find out how the government ensures that mines are satisfactorily rehabilitated. Why might there be a problem with very old mines that have existed for many years?