The Tribune, Chandigarh, India

Waste utilisation: emerging trends
G.S. Dhillon

The activities result in production of large quantities of wastes, both industrial and agricultural, whose effective disposal creates problems. These so-called wastes can be transformed into a resource, but this requires some inputs and efforts using the new technological trends. In this write-up the latest information on the topic is discussed to create greater awareness among the readers.

Agricultural wastes

Rice husk acting as an integral fuel provides in-situ silica for the lime production, when fired at 900-950°C. The material produced is soft powder, having qualities of hydraulic binder cement. The activity of the hydraulic binder increases with increase in its fineness. The setting characteristics of the binder material fall within the requirements of IS: 4031-1988 covering the hydraulic cements. The product obtained has good workability and watertightness that can be used as masonry mortars, for plasters, foundation concrete and concrete for sub-flooring and terracing.

Bagasse ash has been found to possess good puzzolanic characteristic and nearly two-thirds of the silica is carried in the amorphous state. The studies carried out show that quick-setting material is obtained by mixture bagasse ash, 10% cement (OPC), 4% gypsum finely ground (90% material passing 75 micron sieve), gives material suitable for use as mortar and plaster.

Industrial wastes

Phosphogypsum obtained from the fertiliser plants can be used for making good quality paving tiles. Large quantity of this byproduct is obtained during manufacture of phosphoric acid in the form of cake which contains about 15% to 30% free-lime. The main impurities present in the product as obtained affect its setting time and the rate of strength development. The are the under decomposed phosphoric rock, organic matter, quartz and minute amount of radio-activity.

For mass utilisation of the waste, it is imperative to remove or inactivate the impurities present and for the purpose CBRI (Roorkee) has developed a beneficiating process which may involve simple washing or chemical leaching of phosphgypsum, depending on the degree of improvement needed.

The beneficiated material has potential for use as set controller in the cement manufacture process or for production of sulphuric acid.

Fluorogypsum is a byproduct obtained during the manufacture of hydrofluoric acid and it is in the form of anhydrite of calcium sulphate and contains impurities like calcium fluoride and free acids. The fluorogypsum after judicious grinding and blending with chemical additives, can develop high strength (25-30 MPa).

The high strength anhydrite plaster can be used for making gypsum polymer composite, having the properties as: flexural strength of 12 to 14 N/mm2, water absorption 2-3%, wear resistance of 3-4 mm, and porosity value of 5-8%. The gypsum polymer material can be used for preparation of tiles or as replacement for cement and for making ceramic tiles.

Lime sludges in large quantities are obtained as waste or as byproduct from the industries producing sugar, calcium carbide, acetylene, soda ash, tannery and paper. The impurities present in the lime sludge result in poor strength development. These sludges have been used in different ways in the production of cements and cementitious materials.

The lime sludges have also been used in t he manufacture of masonry cement or as replacement of lime powder. CBRI (Roorkee) has found that masonry cement conforming to the requirements of IS: 3466-1988 can be produced from the lime sludges obtained from the acetylene and sugar manufacture.

A rapid-setting activated lime-pozzolana mixture based on the calcined lime sludges and fly-ash or surkhi (conforming to IS: 4098-1988) has been developed by CBRI. The product so obtained has low density, high water rentetivity and low expansion or shrinkage. So it can be used for mortars, and plasters directly after mixing with sand and water.

Blast furnace slags

Ferro alloy and metallurgical slags originate from the process ferrochrome, ferromangnese and ferrosilicate alloys and also from the smelting of zinc and copper. The potential for utilising these slags in the past has been confined to use as fill material and as road making material. The ferrochrome slag has the potential for utilisation as raw material for making Calcium Silicate.

In India about 18 million tonnes of blast furnace slag is produced annually, out of which 5 million tonnes is in the form of granulated material having glossy character and latent hydraulic properties.

Portland Slag Cement (PSC) conforming to requirements of IS: 455-1989 can be obtained from the slag produced by the steel plants. PSC obtained from use of slag from the Rourkela Steel Plant has high manganese content which is beneficial.

PSC is eminently suitable for use in marine and mass concrete construction due to its high sulphate resistance and low heat of hydration, thus making it suitable for water retaining structures and also for river, port and harbour, hot-springs and sewer systems.

SSC (Super Sulphated Cement) has been obtained from use of granulated furnace slag. It has been found that the slag can be activated by using 20-25% of phosphor-fluoro anhydrite as against the recommended value of 10-15% and SSC conforming to IS: 6909-1980 can be obtained.

Advantage of SSC are its low cost with saving in energy, increased resistance to sulphate and low heat of hydration compared to OPC (Ordinary Portland Cement).

Ground granulated blast furnace slag has been used to obtain pressed bricks by activating with hydraulic lime.

Industrial wastes like red mud obtained from the preliminary processing of bauxite during manufacture of aluminum can be used for making bricks. Red mud comprises iron oxide, aluminum oxide, titanium oxide, silicate and sodium oxide and (so has potential for acting as flux or mineraliser in the cement manufacture.

Flyash is obtained at the thermal plants utilising pulverised coal. At present only a small portion of the total flyash produced is utilised in the form of manufacture of bricks (burnt-clay flyash bricks and sand-lime flyash bricks) and PPC (Portland Puzzolana Cement). The characteristic property of flyash as useful material is the lime-reactivity and values ranging between 3.5 to 7 N/mm2 determine good flyash.

Large-scale use of flyash concrete blocks, which are obtained by use of lfyash, quick lime, gypsum and a small quantity of aluminum powder. The components are mixed in high-speed mixers and hydrogen liberated when aluminum powder reacts with lime and aerate the slurry, which is poured in moulds or forms and cured for 8 — 10 hours. the product obtained is light-weight concrete. If the concrete blocks are autoclaved under steam pressure, the product is good for use as building material.

Blue Dust is the tailing from iron mines and has composition similar to iron oxide pigments of mineral origin. Tests prove that this waste product can be used as pigment in the priming paints. The process is low cost and easy and the anti-corrosive prime obtained has good resistance to corrosion and can be applied to all metals surfaces, by brush or through spray. The blue dust used as pigment does not have any adverse effect on its drying time, film thickness and brushability.

Waste marble slurry is produced by units mining marble. In Rajasthan alone there are 4000 units which produce over six million tonnes of slurry which creates disposal problems. It has been found that polymer composites can be produced using the marble slurry. The lamina prepared are cured at pressure of 0.5 MPs for one hour at room temperature, followed by oven curing for 24 hours at 80°C. The product obtained has flexural strength 50% of teak wood and the product is weather resistant, fire retardant (having self-fire extinguishing capability). The technological advances achieved make the product commercially viable.

NEW PRODUCTS & DISCOVERIES

The Greenest PC

Lead, barium, boron, cobalt — these are just a few of the toxic substances that make up the average desktop computer, 10 million of which will end up in landfills worldwide this year.

To lessen the impact on the environment, NEC has developed the PowerMate Eco. It’s made from 100 percent recyclable plastic, contains virtually no toxic substances, and requires just one-third the power of other PCs.

An Eco with a 900MHz Crusoe processor, 20GB hard drive, and 15-inch display costs $1,599. www.nec.com. Popular Science

250-year record of lead pollution

A new study suggests the ebb and flow of North American industry since the dawn of the Industrial Age can be tracked through lead traces found in a 450-foot ice core drilled in Greenland three years ago.

The core contains a high-resolution record of how much lead settled from the atmosphere onto Greenland between 1750 and 1998. The study says the source of the lead appears to have been factories in the United States and Canada.

Lead emissions began to spike in 1870 and had increased 300 per cent just 20 years later, said Joseph McConnell, an associate research professor at the Desert Research Institute in Reno, Nevada.

The 1890 pollution levels were higher than previously thought, suggesting intense levels of both industrial activity and pollution, said McConnell, co-author of the study expected to appear in an upcoming issue of the journal Geophysical Research Letters.

Lead levels plummeted during the Depression in the 1930s, then climbed during the industrial boom that followed World War II, according to the study. That period marked the beginning of the widespread use of lead as a gasoline additive. AP

Sea ice melting fast: NASA

Perennial sea ice that remains year round near the Arctic Circle is melting faster than previously thought and could disappear entirely within this century, according to a study by the National Aeronautics and Space Administration (NASA).

The sea ice is now melting at a rate of 9 per cent per decade, and if these melting rates continue for a few more decades, the sea ice may be completely melted by the end of the century due to rising temperatures and interactions between the ice, ocean and the atmosphere that accelerates the melting process, NASA said in a release.

The melting sea ice would not affect sea levels, but it could profoundly impact summer shipping lanes, plankton blooms, ocean circulation systems and global climate, according to the study.

"If the perennial ice cover, which consists mainly of thick multi-year ice floes, disappears, the entire Arctic Ocean climate and ecology would become very different," said Josefino Comiso, a researcher at NASA’s Goddard Space Flight Centre. PTI

Cameras to monitor lake waters

Italian Space Scientists are developing a prototype of a state-of-the-art portable digital camera that could monitor quality of lake waters on the spot for attending environmental emergencies.

Dr Eugen Zilioli, Head of the Institute of Sensing of Electro Magnetic Energy, Milan Centre under the Italian National Research Council, says that the scientists had secured the required sensors from Helsinki and optical devices from Gelelio of Italy for the purpose.

The camera could take aerial pictures of the lakes on a regular basis and in emergencies from a helicopter or an aeroplane instead of commissioning a remote sensing satellite which involved huge costs and time.

The camera, he said, could cost $ 25,000 and the data inputs had been acquired through a multi-million dollar integrated research project named Satellite Remote Sensing for Lakes Monitoring (SALMON), coordinated by him since 1995. UNI

SCIENCE & TECHNOLOGY CROSSWORD

Clues

Across:

1. Times when Sun is overhead at the Tropics of Cancer & Capricorn.

7. A colourless, odourless, inert gas.

8. Simple lipid consisting of esters of higher fatty acids than those in oils.

9. Hard brittle paraffin wax used in paints and varnishes.

11. ….microscope uses Tyndall effect to see particles not seen with ordinary microscope.

12. Symbol for Iridium.

14. This symbol is used by libraries for books with unknown place of publication.

15. Symbol for Tantalum.

16. Abbr. for a common component of electronic technology.

18. Machine for sawing wood along the grain.

20. Point of zero displacement in a vibrating system.

21. Drug prepared from the fungus.

23. ….glass is kind of gelatin got from Sturgeon.

24. Prefix denoting one million million millionth.

25. Seventeenth Greek letter.

26. Vertical trail of smoke from a chimney.

27. Symbol for Sodium.

Down :

1. Level above which there is always snow.

2. Line which can be drawn through adjacent positions of a point thus tracing the path of the point in space.

3. He defined the second law of refraction.

4. Tendency of a body to preserve its state of rest or uniform motion in a straight line.

5. Institute specialising in innovative joining technology to upgrade industrial products.

6. Disposal of sewage and refuse.

10. A natural blue coloured crystalline transparent corundum.

13. Unwrought or untreated state.

17. Hard skeletons of various marine organisms.

19. Frame holding glass in window.

22. Outer face edge of a dam.

Solution to last week’s Crossword: