“We are exporting foundry grade chromite sand and the requirement for the product is that the silica has to be less than one per cent. As we all know chromite is an important raw material in South Africa as chrome mining in South Africa facilitates half the world’s production of chrome ore. Foundry grade chromite sand is the main ore source for ferro-chrome manufacturing and also makes up to 80 per cent of the world’s chromite sand used in foundries,” explained Manfred Rosch, MD of Refraline.

“The silica is in the raw material as a separate grain and by crushing the ore it is loosened and then it has to be separated. Normally this is done by washing it out in the wet process. The raw material runs down a spiralling process and through the movement the lighter silica is separated. This could take up to five and more spiralling and washing processes whereas the lighter silica material rises to the top and each time it is ‘scooped’ off and the heavier chromite material remains for further processing.”

“We were already exporting chromite sand and looked at investing in our own plant. Due to the many environmental issues, including regulations for the water treatment plant, licences and other protocols, we became interested in the dry process to manufacture foundry grade chromite sand.”

Refraline have installed a magnetic separator to produce foundry grade chromite sand via the ‘dry’ method. The plant has been setup at Refraline’s existing facility in Richards Bay, Kwa-Zulu Natal where the company produces castables mainly for export and they also crush and screen aluminium alloys as an improvement material used in the manufacture of castables

“Foundry grade chromite sand is a complex compound of various elements; chromium (Cr2O3), iron oxide (Fe2O3), aluminium (Al2O3), silica (SiO2), and magnesium oxide (MgO). Chrome’s resilient characteristics make it the material of choice for many foundry applications. It is used in moulds for automotive castings and as a well filler in steel production.”

“At the 2019 GIFA in Düsseldorf, Germany we saw a magnetic separator on display on the Omega Sinto stand. The magnet used in the process is not your normal magnet. Those used are Neodymium magnets and they are a member of the rare earth magnet family and are the most permanent magnets in the world.”

“The magnet detects the iron, which is part of the raw material, and it therefore attracts the chromite. In that way you can separate the chromite from the silica. It is a technology that is widely available worldwide.”

“It is not a first in South Africa as the process is already used in sand reclamation in the foundry. Sand reclamation is used in foundries, as it promotes the reuse of spent chromite sand and saves on disposal costs. Every foundry with a reclamation plant aims to remove as much chromite sand from the reclaimed silica sand as possible (prior to thermal reclamation). The use of magnets in the reclamation process is very beneficial to aid the process because there is a bigger percentage of silica in the used sand as compared to when you are manufacturing foundry grade chromite sand. You are talking of a higher percentage in silica sand reclamation as compared to about 5% in beneficiation of chrome sand to foundry grade manufacture.”

“The separation is carried out using a magnetic separator as the chromite sand can be weakly magnetised. Permanently magnetic, high-intensity separators are used in combination with cleaning and dust-removal devices.”

The plant consists of a magnetic separator, a classifier and a density separator. These were all manufactured and installed by Omega Sinto’s subsidiary in South Africa Endeco Omega Sinto

“In comparison with quartz sand, chromite sand has a higher temperature resistance and better thermal conductivity. These attributes make the mould material especially suitable for mould areas with high material accumulation and for materials with high casting temperatures, for example in steel casting. On the one hand, chromite sand guarantees high quality for certain casting products, on the other hand, this kind of sand increases the cost of moulding material, if there is no internal circulation system. Chromite sand is considerably more expensive than quartz sand.”

“The mixture of chromite sand and quartz sand which arises inevitably at the shake-out grid usually leads to problems with the quality of the casting, as well as increased costs, when reused. For this reason, these sand varieties must be separated and put back into the mould material cycle separately.”

“As chromite sand is slightly magnetic, modern systems separate chromite sand from quartz sand in a way that results in very pure materials, so that it can flow back into the mould and core production process as a replacement for new sand.”

“When we visited Omega Sinto they said our idea was possible and they did tests at a pilot plant as they have not done this before. There were delays in the construction of the plant as the magnets had a long lead time. However then plant is commissioned and running, as we are producing to ramp up production

“It is not necessarily a better product using our dry method production process compared to spiralling except that in spiralling they do not use fresh water, which effects the turbidity. The turbidity of chromite sand is always critical. The reuse of water could allow for more impurities to end up in the product whereas with the dry process method you vacuum all of the impurities out of the final product.”

“We are going to supply the product to all markets with the international market being bigger than the local market. In the first phase we are going to produce 500 tons a month. The plant is setup to install another line and when demand necessitates it, we could be producing 1 500 tons to 2 000 tons per month.”

“Before beneficiating we obtain our raw materials from local mines and from neighbouring countries in the Southern African region.”

“Using our dry process the price per ton might not necessarily be an advantage. However, where we do have an advantage is that if there is no foundry grade available we can use met grade. Using our dry process we can process this met grade into foundry grade.”

“The specification of the foundry grade is critical as you have to make sure your AFS is correct as well as your chemical analysis and turbidity. We can also produce special grades as there is some call for this nowadays.”

Refraline has developed a range of monolithic refractory materials, which has undergone significant testing. The company focus is on design and development of refractory materials, demolition, maintenance and repair of refractories, corrosion engineering solutions, materials and maintenance and lagging and cladding installation and repairs

“We have an existing plant in Richards Bay, Kwa-Zulu Natal where we produce castables mainly for export and we also crush and screen alumina-silica bricks as a material used in the manufacture of our castables. There was enough space to locate the new plant on our existing premises and we are now producing foundry grade chromite sand and exporting to Malaysia, Germany, Columbia and Chile already.”

“The plant basically consists of a magnetic separator, a classifier and a density separator.”

“These were all manufactured and installed by Omega Sinto’s subsidiary in South Africa Endeco Omega Sinto.”

“Chrome sand is the perfect material for hot metal casting, it is also an excellent ladle filler preventing contact between the molten steel and the ladle slide gate system. Chrome sand is also used in the production of magnesite chrome refractory bricks which usually contain over 33% of chromium and in the manufacture of chrome conundrum refractory bricks, providing resistance to abrasion and high temperature. Chrome sand is extensively used in casting moulds given its high thermal conductivity and low thermal expansion properties.”

Established in 1981, Refraline has grown from strength-to-strength over the decades, and is today recognised as one of the leading refractory and corrosion contracting companies in South Africa, employing a core workforce of more than 300 permanent skilled staff and is supplemented by a substantial pool of temporary personnel.

Refraline has developed a range of monolithic refractory materials, which has undergone significant testing. The company focus is on design and development of refractory materials, demolition, maintenance and repair of refractories, corrosion engineering solutions, materials and maintenance and lagging and cladding installation and repairs.

Refraline delivers product and services to most industries in South Africa and exports to many countries worldwide. Included in these industries are the iron and steel industries, the foundry industry, the ferro alloy industry and the non-ferrous industries. The company’s R&D facility enables it to develop customer-specific refractory materials and set new trends.

The Refraline Group of Companies consists of Refraline, Refraline Natal, DCE Corrosion Engineering, Refraline Northern KZN and RefNtombi, with its headquarters situated in Meadowdale, Germiston, Gauteng.

For further details contact Refraline on TEL 011 392 0700 or visit www.refraline.com