XXV International Mineral Processing Congress (IMPC 2010) Eco-Efficient Gravity Separation Solutions in India Carlos A. Pena Reference Number: 441 Contact Author: Full name Carlos A. Pena Position title Business Development Manager Organisation Name Mineral Technologies Address 11 Elysium Rd, Carrara, Qld, 4211 Phone 07 5569 1317 Fax 07 5525 3810 Mobile 0448 417 786 Email [email protected]
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Eco-Efficient Gravity Separation Solutions in India
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XXV International Mineral Processing Congress (IMPC 2010)
Eco-Efficient Gravity Separation Solutions in India
Carlos A. Pena
Reference Number: 441 Contact Author: Full name Carlos A. Pena Position title Business Development Manager Organisation Name Mineral Technologies Address 11 Elysium Rd, Carrara, Qld, 4211 Phone 07 5569 1317 Fax 07 5525 3810 Mobile 0448 417 786 Email [email protected]
Eco-Efficient Gravity Separation Solutions in India
Carlos Pena1
1. Business Development Manager, Mineral Technologies, 11 Elysium Road, Carrara QLD 4216, [email protected]
ABSTRACT Sustainable development and social responsibility issues are a principal aspect of mineral
processing operations around the world. With the need for more environmentally effective
technologies, some gravity separation systems have provided eco-efficient mineral processing
solutions in places where it is not otherwise viable because of lack of fresh water or for other
environmental reasons. Advanced spiral separation technologies developed in Australia offer a
cost effective and environmentally viable way to process minerals. In particular, we review recent
case studies of spiral plants commissioned in India where environmentally sustainable solutions
to design problems included the use of spirals operated with sea water and the use of high
capacity (HC) spirals to provide low consumption of energy and materials and a reduced plant
footprint. This paper evaluates the performance of various spiral plants in India and how critical
environmental issues which affect the overall viability of wet concentrating processes where
resolved.
Keywords: Spiral separators, Gravity Concentration, Sea water mineral processing
INTRODUCTION India is home to a myriad of metals and minerals. Globally, the country is the largest producer of
sheet mica, the third largest producer of coal, the fourth largest producer of iron ore, the fifth
largest producer of bauxite and one of the largest producers of mineral sands in the world.
India’s mining industry continues to grow in economic importance. A report from Business Monitor
International, noted that India has significant amounts of natural resources, which should allow it
to develop a world-class mining industry.
The country clearly has massive potential but at present there are a host of problems to
overcome, including poor levels of resource recovery, sluggish geological exploration and
environmental damage from mining and mineral processing.
India having 18% of the world's population on 2.4% of world's total area has greatly increased the
pressure on its natural resources. Water shortages, soil exhaustion and erosion, deforestation, air
and water pollution afflicts many areas. In fact, India is at risk of severe environmental problems.
Many of its rivers are heavily polluted and fresh water sources limited, raising questions about the
sustainability of the mining sectors rapid growth.
In February 2009, the 20th National Convention of Mining Engineers in India emphasized the
importance of clean mining technologies, to help decrease the environmental effects of mining.
With the need for more environmentally effective and clean mining technologies, some gravity
separation systems have provided eco-efficient mineral processing solutions in places where it is
not otherwise viable in India because of lack of fresh water or for other environmental reason.
Advanced spiral separation technologies have offered a cost effective and environmentally viable
way to process minerals in India. Recent projects to process mineral sands in the state of Tamil
Nadu India have been viable thanks to the use of spiral separators processes using sea water.
This paper explores some recent projects where these technologies made the projects
environmentally viable.
Most of the metallurgical data and findings contained in this paper come from working closely with
V.V. Mineral, one of our main clients in the state of Tamil Nadu, and India's largest miner,
manufacturer and exporter of Garnet & Ilmenite. For a number of years, Mineral Technologies
has closely worked with VV Minerals to provide mineral processing solutions at their different
facilities located in Tamil Nadu India.
Water issues for mining in India Water shortages are a serious problem for mining companies in India. In a recent survey of
India’s water situation, Fred Pearce reported that the 21 million wells drilled in recent years are
lowering water tables in most parts of the country. From 1947 to 2002, average annual per capita
water availability declined by almost 70% to 1,822 cubic meters.
Tamil Nadu, located in the southeast tip of India and where we have focused the findings for this
paper, is a water-scarce state with a vast mining potential. In addition to mineral sands, the state
has diverse potential of minerals such as limestone, lignite, granite, clay, gypsum, feldspar,
graphite, and iron. Small quantities of gold, copper, kaolin, bauxite, and asbestos are also
available.
Even though Tamil Nadu has 33 river basins, the rivers are short, and carry water seasonally
making most of these mining projects unviable.
In addition to this, the state has a population of more than 62 million people, wells have been
drying up at a rampant rate and falling water tables have dried up 95 per cent of the wells owned
by small farmers thus reducing the irrigated area in the state by half over the last decade. In
communities where underground water sources have dried up entirely, all agriculture is rain-fed
and drinking water is trucked in.
Mineral Sands deposits in Tamil Nadu - India
Heavy mineral sand deposits consist of sand accumulations that contain significant amounts of
heavy minerals (generally defined as minerals with a specific gravity greater than 2.8SG).
Contained heavy minerals occur as disseminated, associated or concentrated deposits within the
sands and often include titanium minerals, zircon, garnet and sillimanite.
In India, exploration for, and extraction and processing of heavy mineral sands has intensified in
recent years due to increasing use and demand for titanium oxides, metals and alloys. Zircon
formerly viewed as a by product has now been a target in light of strong markets, especially
China during the years of strong construction growth.
The coastal districts of Kanyakumari, Tirunelveli, Thoothukkudi, Nagapattinam and
Ramanathapuram in Tamil Nadu are endowed with high quality heavy mineral placers such as
Garnet, Ilmenite, Rutile, Leucoxene, Monazite and Zircon. They have wide use in pigment,
refractory, ceramic industries and nuclear industry world wide.
The Department of Geology and Mining of the Government of Tamil Nadu,estimates reserves of
these deposits at about 23 million tonnes of Garnet, 98 million tonnes of Ilmenite, 5 million
tonnes of Rutile, 2 million tonnes of Monazite and 8 million tonnes of Zircon. The major players
are the Indian Rare Earths (IRE), a Government of India Undertaking, V.V. Minerals, Beach
Mineral Company, Transworld Garnet and Indian Ocean Garnet Sand.
Mineral Sands processing with spirals in Tamil Nadu – India Gravity concentration of minerals in India has traditionally been recognized as a low cost and
environmentally friendly process for the separation of minerals. Spirals separators are simple, low
energy consuming devices that separate minerals based on their respective densities and have
proven to be metallurgically efficient and cost effective since their widespread commercial
introduction more than 60 years ago.
Mineral sands processing in Tamil Nadu usually consists of wet and dry processes to extract
mineral concentrates. A typical wet plant will consist of pumping, hydrocyclones for desliming,
surge bins, spirals, up current classifiers and wet magnetic separation (Figure 1)
Wet plants in India are usually fed with water directly sourced from the sea with pumps located
near the coast line (Figure 2).
Process water ponds which handle sea water are specially lined with concrete ensuring the sea
water doesn’t infiltrate the ground. Spiral tailings are treated through hydrocyclones and the
overflow water recovered and sent to tailing ponds. Only 5-10% of the process plant water
reports with the final HMC and tailings which are again handled in concrete lined ponds. Water
overflow is recovered and sent back to the process water ponds.
In the case of VV Mineral they operate 8 spiral separation plants (Figure 3) which stretch from
Kanyakumari to Tuticorin near the coastline of Tamil Nadu.
Total spiral plant processing capacity at VV Minerals operations is 1,180tph made up of eight
plants with feed rates varying from 40 tph to 500 tph as detailed below:
• Three 120 tonnes per hour feed plant
• One 40 tonne per hour feed plant
• One 50 tonne per hour feed plant
• One 80 tonne per hour feed plant
• One 150 tonne per hour feed plant
• One 500 tonne per hour feed plant
Sea water vs. fresh water spiral performance A series of tests to determine the variance in spiral performance when operated with either fresh
water or sea water were carried out at VV Minerals operations over a two month period. The
trials utilized MG6.3 and HG10 spiral separators.
A series of 8 tests were carried out on the two spiral models at feed rates varying between 1.2 to
2.1 tph. Pulp density fed to the spirals varied within the range of 35.7% and 41.7% solids (w/w).
As the tests were carried out in an operating plant environment there were inevitable variations in
the feed conditions throughout the tests. In some tests the spirals were operated at higher feed
rates on the salt water slurry. In the case of the HG10, the spiral was operated at 2.0 t/h on fresh
water whereas it was run at 2.4 t/h on salt water. This is a 20% increase, which is significant. In
the case of the MG6.3, the feed rate was 2.7 t/h on fresh water and 11% higher at 3.0 t/h on sea
water.
Overall there was no conclusive difference in performance between salt water and fresh water
processing on the MG6.3 and HG10 spirals (once variations in feed conditions were taken into
account) (figure 4). While this result is perhaps not surprising given that there is very little
difference in viscosity or specific gravity between salt water and fresh water it does further
reinforce the viability of using low quality water in spiral separation plants.
The use of sea water, or highly saline water, will naturally increase the potential for corrosion in
and around the processing plant and may reduce the life of the plant if a high level of corrosion
protection is not maintained. Spiral separators however are manufactured from fibreglass with a
highly resistant polyurethane surface and are far less susceptible to corrosive attack in such
environments.
Fresh water savings in the spiral plants at VV Mineral The average water requirement for a spiral plant is between 0.15 – 0.18 tph of water per tonne of
solids feed. The total spiral plant capacity at VV Mineral is 1,180 tph for the 8 plants currently in
operation. Taking this into consideration and with the use of sea water in their process, fresh
water savings at VV Minerals run in the order of 4,248,000 litres per day.
According to the Stockholm International Water Institute, 100 litres a day is the minimum per
capita water requirement for India’s basic domestic needs. With this in mind VV Mineral’s fresh
water savings provide an availability of fresh water per day for 42,480 people in the Tamil Nadu
State.
In addition to this, the use of sea water in these plants has allowed for the viability of these
projects that generate employment for local workers in the order of 3,400 direct employments
High Capacity spirals (HC Spirals) Ongoing research and development efforts have improved separation efficiencies of spiral
models over the years. Improvements in materials of manufacture have reduced weight and
enhanced operational capabilities.
The concept of a high capacity, small footprint processing plant has now been successfully
commercialized in recent mineral sands and iron ore projects. In some cases a small footprint,
high capacity plant was necessary to make projects viable.
Modern high capacity spiral models can process up to 35 tph per quad start spiral. In some cases
both the rougher and scavenger processing stages are incorporated into the same spiral.
Conventional spiral separators can process up to 9 tph per triple start spiral.
Combining rougher and scavenger stages of separation into one unit obviates the need for
intermediary equipment including feed sumps, pumps and motors, electrics, laundering and feed
distribution systems. The introduction of two stage high capacity spirals into the industry has
allowed the reduction of plant foot prints to just 40% of the area of plants designed based on