A Barmac vertical shaft impactor crusher for iron ore? The innovativeness of JSW Steel not only makes this possible, but also demonstrates the benefits an unconventional circuit can bring.
JSW Steel is the largest integrated private steel manufacturer in India in terms of installed capacity and one of the lowest cost steel producers in the world. In 1997, when JSW started its iron ore beneficiation plant, the plant´s production was only 1.5 mt. Since then, the growth has been exponential and there has been no looking back. In 2007, JSW started working with their available resources to make a breakthrough with ore upgradation. After testing the ore in-house, they discovered that they were able to generate sinter fines as well as pellet fines. The testing also revealed a recovery rate of around 70 per cent for the pellets and the sinter fines a green light for the company to further expand its production. The constantly declining ore grades meant that they had to get equipment that could upgrade ores of lower value than before. ´We tried upgrading feed Fe 45-49 grade, which is mainly the waste from the mines. This material is brought to our plant, and we are achieving upgradation of up to 57.5 per cent. From these lower grade ores, we are getting 56.5-58.5 Fe grade in the sinter and pellet concentrates,´ says Harvendra Diwan, Associate Vice President (BP-2), JSW Steel.
A technology overhaul JSW couldn´t achieve these results with the conventional circuit for iron ore beneficiation, so it decided to create its own circuit based on pure mathematical calculations. As a result, the JSW iron ore beneficiation plant is nothing short of a wonder when it comes to experimenting with technology. When they started looking for suitable equipment for the ground work, they went to the Metso website and studied Metso´s Barmac Series Vertical Shaft Impactor crushers. They realised that this crusher might be able to provide a dual crushing and grinding effect. So, as a next step, Metso was consulted. This was the first time a VSI would be used for processing iron ore. ´We wanted a crusher that could give us a good size; so when we saw Metso´s Barmac, we anticipated that this might be the best crusher for the job,´ recalls Diwan. The ore was then sent to Metso for testing to see whether the Barmac would work or not. The results were very positive, and, for the first time ever, a Barmac was installed for iron ore processing. After the installation, JSW´s attention shifted to finding the right Scrubber for the circuit. ´We selected Metso´s attrition scrubber for the feed size. We realised that if you crush more than 3 mm, chances are that the attrition scrubber will get jammed. Because we selected the Attrition Scrubber, the product size from the Barmac was restricted to -3 mm. As of now, the Barmac is fed 40 mm that get reduced to -3 mm,´ Diwan explains. This was another first in the industry. Nobody before JSW has used an attrition scrubber for iron ore processing. The chemical composition of the ore makes is such that, without liberation, beneficiation is difficult. Hence a few alterations in the circuit can bring about a world of change in the quality of product and the ability to convert low-grade iron ore to high grade.
An extra challenge from the softness of the ore. The selection of equipment depends on the softness of the ore, and the Karnataka ore that JSW has to work with is very soft. Grinding that kind of an ore generates more ultra fines (-10 microns), which makes separation of the ore very difficult. That´s where the metso high gradient magnetic separator (HGMS) technology comes into action. The Metso HGMS is the only machine that can capture such a low grade of iron ore and ultra fines for separation. Looking at the performance of the HGMS, JSW decided to place it too in the main beneficiation plant.
´We loved our experimental results and dared one brave step after another. Right now we are feeding 37-38 grade Fe into the HGMS and getting 59-60 Fe with a recovery of 22 percent. And, in general, the Metso HGMS can also give a recovery of 68-70 per cent. Considering the kind of performance the HGMS gives, the payback period will be 6-7 months and the profits on top of that are commendable,´ says Diwan.
So, what is it about the HGMS that can almost work miracles for ore separation? ôThe uniqueness of the HGMS lies in its magnetic strength,´ explains R Harish, Senior Manager-Sales, Process Equipment, Metso India. ´Variables like pulp flow velocity and matrix loading are something that cannot be found in an HGMS of any other make. These variables help you to customise on the mechanism and enhance the recovery. Even the JSW circuit can be taken as an example. Currently, feed to the HGMS in the circuit is basically the Jig and spiral tailings. They can even use the HGMS in the main beneficiation circuit to recover maximum Fe from the plant tailings.´
´Metso also put in a lot of effort along with us so that we could achieve positive results; and that cooperation is something you can´t overlook,´ adds Diwan. Spiraling for straight recovery given the softness of the Karnataka ore, it takes two stages for the ore to be separated. What JSW did for that was to place Spiral Concentrators in the circuit for pre-separation before putting it in the HGMS for further processing.
´If you grind the soft ore available in Karnataka in a single stage, you´ll only get about 50-55 per cent recovery. But by introducing grinding stages and spirals in the circuit, we are able to increase overall recovery by 15 per cent. If you´re recovering 15 per cent more material, you are saving on costs and requiring less material for tailing, and also the water recovery is possible, which means more profit in the long run. This will help lower prices and cater to the never ending demand of the steel industry,´ Diwan explains. Turning low-grade ore into high grade is a must In light of the recent bans on mining, it has become more imperative for Indian iron ore producers to look at a technology that can beneficiate very low-grade iron ore to high-grade iron ore.
Getting the right results requires the right equipment. Even for JSW, building the circuit was a gradual, step-by-step process. ´You have to be very careful when setting up a beneficiation plant, because the wrong set of equipment can upset things very badly. Initially, JSW bought some equipment and then gradually kept adding equipment according to the product requirements to make sure that we got what we wanted,ö says Diwan.
Part of the JSW Group
The largest integrated private steel manufacturer in India, interms of installed capacity
Spread over six locations in India and a footprint that extends to the US, South America and Africa
JSW´s history dates back to a single steel mill in 1982
Metso equipment supplied for beneficiation plant
Barmac VSI crushers - 14 units (commissioned 12)
Grinding mill (Ball mills) - 1 unit
Spiral concentrator - 63 banks
HGMS - 3 units
Attrition Scrubbers - 14 units (commissioned 12)
Slurry pumps - 43 units
Courtesy: Results - Minerals & Aggregates, Metso India