Water related issues, regarding both quantity and quality, are casting a shadow on India’s push towards the future. Government authorities, accordingly, are tightening the regulations on how water is used, and who gets to use it.
This concern for water is also a growing priority for India’s mining companies. Mining products are needed for India’s growth, but mining has always been an industry that has a big impact on water. Sometimes through de-watering that reduces water tables and therefore groundwater supply in neighbouring areas, through its need for process water and in many cases for water-covered tailings storage facilities (TSFs). There is also a risk from traditional TSFs failing, causing flooding and other downstream impacts.
Because mining faces these issues worldwide as well, ways to reduce water impacts are being eagerly sought and implemented.
Part of the solution, seeing growing application in India and elsewhere, comes through “thickened tailings” in which the finely-ground waste rock produced by the mine’s milling process is engineered to a thicker consistency. This changes its consistency from slurry (water containing dissolved and suspended powder) to a product with a consistency much like toothpaste. While conventional tailing slurries are about 30 to 50 percent solids by mass, thickened tailings can range between 65 and 80 percent solids. Thickening tailings can reduce the amount of water in the tailings mass by about 85%. Thickened tails, often called “paste”, has many potential benefits particularly with regards to water impacts:
* Because the water removed in the thickening process is usually circulated back to the mine or mill for re-use, the amount of process water needed is lessened
* The tailings form an inert mass, so there is less potential for precipitation to leach salts and metals into watercourses
* After a layer of thickened tailings has been allowed to dry, more can be spread on top, with further layers added – reducing the surface area required – and the tailings can be vegetated and even farmed
* In a TSF you can simply place more thickened tailings than conventional slurry tailings – reducing the size of land take
* Thickened tails can be pumped back underground into disused underground openings (paste backfill), reducing the need for other slurry backfill, improving productivity, reducing cement costs while also reducing surface impacts
* Surface and underground deposition of thickened tailings can reduce or eliminate the need for a conventional sub-aqueous disposal, reducing long term costs and particularly, post-closure legal obligations and liabilities.
Thickened tailings is not suitable for all situations. The grain size selected by the mill to optimize ore recovery may not be suitable for thickening. Other factors, such as mica content, may also influence whether the tailings are suitable. The available water may not have the purity needed for the process.
The up-front costs of the equipment may be slightly higher than for a conventional sub-aqueous TSF, but when medium and long-term operating costs are factored in, the total costs are often noticably lower – particularly when adding in the post-closure maintenance obligations and legal liabilities. Personnel with the right experience and skills are needed to set up the system and operate while developing local personnel skills to take over ongoing operations and maintenance. As thickened tailings increases in popularity, finding the right employees is becoming less of a problem.
A large part of success in thickened tailings comes from being able to consistently produce a product that meets design criteria regarding viscosity, water content and other variables. If it does not, there may be excessive water flowing from the disposal area, or there may be excessive strain and wear on pumps and other equipment. Correct product consistency is particularly important in underground disposal, where the tailings are used to support a mined-out stope so that the rock next to it can be worked on.
Having appropriate professional support, either from inside or outside the mining company, can go a long way to determining whether thickened tailings is a viable solution in any given situation, and in maximizing the benefits if this technology is chosen.
Paste technology helps coal-fired plants manage ash
Coal-fired power generation is important to helping India meet its power needs. However, the coal available in India tends to produce a relatively high ash volume, and this waste must be disposed of. Government regulations, and the need to reduce the amount of land required for disposal, are driving an interest in paste technology. One of the chief benefits of thickening the ash into a form that dries to provide an inert mass is that the waste can be stacked higher than otherwise, so that less land is consumed.
Golder Associates has worked with power producers in North America to help with fly and bottom ash disposal through thickening. This technology is showing good promise for ash disposal – particularly attractive as the surface can be cultivated after disposal is finished. Golder has held discussions with major producers directly as well as examining opportunities with major India EPCM contractors in this sector.
Russell Merz is with Golder Associates Consulting India Pvt Ltd, based in Haryana, India, part of a global company focusing on geotechnical engineering and environmental sciences. Contact: rmerz@golder.com; tel. 9811682754.
Nick Slade is Vice President Consulting with Golder Paste Technology Ltd (a subsidiary of Golder Associates), based in Falmouth, UK. Contact: nslade@golder.com; +44 1326 211470.
This concern for water is also a growing priority for India’s mining companies. Mining products are needed for India’s growth, but mining has always been an industry that has a big impact on water. Sometimes through de-watering that reduces water tables and therefore groundwater supply in neighbouring areas, through its need for process water and in many cases for water-covered tailings storage facilities (TSFs). There is also a risk from traditional TSFs failing, causing flooding and other downstream impacts.
Because mining faces these issues worldwide as well, ways to reduce water impacts are being eagerly sought and implemented.
Part of the solution, seeing growing application in India and elsewhere, comes through “thickened tailings” in which the finely-ground waste rock produced by the mine’s milling process is engineered to a thicker consistency. This changes its consistency from slurry (water containing dissolved and suspended powder) to a product with a consistency much like toothpaste. While conventional tailing slurries are about 30 to 50 percent solids by mass, thickened tailings can range between 65 and 80 percent solids. Thickening tailings can reduce the amount of water in the tailings mass by about 85%. Thickened tails, often called “paste”, has many potential benefits particularly with regards to water impacts:
* Because the water removed in the thickening process is usually circulated back to the mine or mill for re-use, the amount of process water needed is lessened
* The tailings form an inert mass, so there is less potential for precipitation to leach salts and metals into watercourses
* After a layer of thickened tailings has been allowed to dry, more can be spread on top, with further layers added – reducing the surface area required – and the tailings can be vegetated and even farmed
* In a TSF you can simply place more thickened tailings than conventional slurry tailings – reducing the size of land take
* Thickened tails can be pumped back underground into disused underground openings (paste backfill), reducing the need for other slurry backfill, improving productivity, reducing cement costs while also reducing surface impacts
* Surface and underground deposition of thickened tailings can reduce or eliminate the need for a conventional sub-aqueous disposal, reducing long term costs and particularly, post-closure legal obligations and liabilities.
Thickened tailings is not suitable for all situations. The grain size selected by the mill to optimize ore recovery may not be suitable for thickening. Other factors, such as mica content, may also influence whether the tailings are suitable. The available water may not have the purity needed for the process.
The up-front costs of the equipment may be slightly higher than for a conventional sub-aqueous TSF, but when medium and long-term operating costs are factored in, the total costs are often noticably lower – particularly when adding in the post-closure maintenance obligations and legal liabilities. Personnel with the right experience and skills are needed to set up the system and operate while developing local personnel skills to take over ongoing operations and maintenance. As thickened tailings increases in popularity, finding the right employees is becoming less of a problem.
A large part of success in thickened tailings comes from being able to consistently produce a product that meets design criteria regarding viscosity, water content and other variables. If it does not, there may be excessive water flowing from the disposal area, or there may be excessive strain and wear on pumps and other equipment. Correct product consistency is particularly important in underground disposal, where the tailings are used to support a mined-out stope so that the rock next to it can be worked on.
Having appropriate professional support, either from inside or outside the mining company, can go a long way to determining whether thickened tailings is a viable solution in any given situation, and in maximizing the benefits if this technology is chosen.
Paste technology helps coal-fired plants manage ash
Coal-fired power generation is important to helping India meet its power needs. However, the coal available in India tends to produce a relatively high ash volume, and this waste must be disposed of. Government regulations, and the need to reduce the amount of land required for disposal, are driving an interest in paste technology. One of the chief benefits of thickening the ash into a form that dries to provide an inert mass is that the waste can be stacked higher than otherwise, so that less land is consumed.
Golder Associates has worked with power producers in North America to help with fly and bottom ash disposal through thickening. This technology is showing good promise for ash disposal – particularly attractive as the surface can be cultivated after disposal is finished. Golder has held discussions with major producers directly as well as examining opportunities with major India EPCM contractors in this sector.
Russell Merz is with Golder Associates Consulting India Pvt Ltd, based in Haryana, India, part of a global company focusing on geotechnical engineering and environmental sciences. Contact: rmerz@golder.com; tel. 9811682754.
Nick Slade is Vice President Consulting with Golder Paste Technology Ltd (a subsidiary of Golder Associates), based in Falmouth, UK. Contact: nslade@golder.com; +44 1326 211470.
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