Researchers from the Indian Institute of Technology in Hyderabad have discovered that fly ash - a waste byproduct of power plants that poses a threat to the environment - can be modified into waterproofing material.

The researchers converted fly ash into waterproofing material by treating it with stearic acid, which is commonly used in soaps and shampoos.

Stearic acid is a surface-active agent whose key ingredient binds to dirt particles during the process of washing, while its hydrophobic or water-repelling part remains free. As a result, dirt particles bound with stearic acid separate out just like oil separates from water.

Fly ash

* Fly ash is a coal combustion product that is composed of particulates (fine particles of burned fuel) that are driven out of coal-fired boilers together with flue gases. Ash that falls to the bottom of the boiler’s combustion chamber (commonly called a firebox) is called bottom ash.

* In modern coal-fired power plants, fly ash is generally captured by electrostatic precipitators or other particle filtration equipment before the flue gases reach the chimneys. Together with bottom ash removed from the bottom of the boiler, it is known as coal ash.

* Depending upon the source and composition of the coal being burned, the components of fly ash vary considerably, but all fly ash includes substantial amounts of silicon dioxide (SiO2) (both amorphous and crystalline), aluminium oxide (Al2O3) and calcium oxide (CaO), the main mineral compounds in coal-bearing rock strata.

* The minor constituents of fly ash depend upon the specific coal bed composition, but may include one or more of the following elements or compounds found in trace concentrations (up to hundreds ppm): arsenic, beryllium, boron, cadmium, chromium, hexavalent chromium, cobalt, lead, manganese, mercury, molybdenum, selenium, strontium, thallium and vanadium, along with very small concentrations of dioxins and PAH compounds. It also has unburnt carbon.

* In the past, fly ash was generally released into the atmosphere, but air pollution control standards now require that it be captured prior to release by fitting pollution control equipment. In the US, fly ash is generally stored at coal power plants or placed in landfills. About 43 per cent is recycled, often used as a pozzolan to produce hydraulic cement or hydraulic plaster and a replacement or partial replacement for Portland cement in concrete production.

* In the case that fly (or bottom) ash is not produced from coal, for example when solid waste is incinerated in a waste-to-energy facility to produce electricity, the ash may contain higher levels of contaminants than coal ash. In that case, the ash produced is often classified as hazardous waste.

Health effects of toxins found in coal ash

Lead: The exposure of lead in coal ash can cause major damage to the nervous system. Lead exposure can lead to kidney disease, hearing impairment, high blood pressure, delays in development, swelling of the brain, haemoglobin damage and male reproductive problems. Both low and high levels of lead exposure can cause harm to the human body.

Cadmium: When coal ash dust is inhaled, high levels of cadmium is absorbed into the body. More specifically, the lungs directly absorb cadmium into the bloodstream. When humans are exposed to cadmium over a long period of time, kidney and lung diseases can occur. In addition, cadmium exposure can be associated with hypertension. Lastly, chronic exposure of cadmium can cause bone weakness, which increases the risk of bone fractures and osteoporosis.

Chromium: The exposure of chromium in coal ash can cause lung cancer and asthma when inhaled. When coal ash waste pollutes drinking water, chromium can cause ulcers in the small intestine and stomach when ingested.  Lastly, skin ulcers can also occur when chromium in coal ash comes in contact with the skin.

Arsenic: When high amounts of arsenic is inhaled or ingested through coal ash waste, diseases such as bladder cancer, skin cancer, kidney cancer and lung cancer can develop. Ultimately, exposure to arsenic over a long time can cause mortality. Furthermore, low levels of arsenic exposure can cause irregular heartbeats, nausea, diarrhoea, vomiting, peripheral neuropathy and vision impairment.

Mercury: Chronic exposure of mercury from coal ash can cause harm to the nervous system. When mercury is inhaled or ingested, various health effects can occur such as vision impairment, seizures, numbness, memory loss and sleeplessness.

Boron: When coal ash dust is inhaled, the exposure of boron can cause discomfort in the throat, nose and eye. Moreover, when coal ash waste is ingested, boron exposure can be associated with kidney, liver, brain, and intestine impairment.

Molybdenum: When molybdenum is inhaled from coal ash dust, discomfort of the nose, throat, skin and eye can occur. As a result, short-term molybdenum exposure can cause an increase of wheezing and coughing. Furthermore, chronic exposure of molybdenum can cause loss of appetite, tiredness, headaches and muscle soreness.

Thallium: Exposure to thallium in coal ash dust can cause peripheral neuropathy when inhaled. Furthermore, when coal ash is ingested, thallium exposure can cause diarrhea and vomiting. In addition, thallium exposure is also associated with heart, liver, lung and kidney complications.

Silica: When silica is inhaled from coal ash dust, fetal lung disease or silicosis can develop. Furthermore, chronic exposure of silica can cause lung cancer. In addition, exposure to silica over a period of time can cause loss of appetite, poor oxygen circulation, breathing complications and fever.

Uses of fly ash

* Concrete production, as a substitute material for Portland cement and sand

* Embankments and other structural fills (usually for road construction)

* Grout and flowable fill production

* Waste stabilisation and solidification

* Cement clinkers production - (as a substitute material for clay)

* Mine reclamation

* Stabilisation of soft soils

* Road sub base construction

* As aggregate substitute material (for brick production)

* Mineral filler in asphaltic concrete

* Agricultural uses: soil amendment, fertiliser, cattle feeders, soil stabilisation in stock feed yards and agricultural stakes

* Loose application on rivers to melt ice

* Loose application on roads and parking lots for ice control