Skullduggery

This is not your usual quarry operation, but this method of retrieving scrap steel and iron from steel mill sites is common around the world as the price and demand for steel continues to soar.  BY ALAN TITCHALL

It’s a quarrying process like no other, says SteelServ Business manager Keith Grala as we look over a mound of pulverised scrap iron about to be returned to the steel foundry.

“With a value of $800 a tonne, this is a very valuable part of the steel making process.”

It’s a process that has been on going at the Glenbrook Steel Mill south of Auckland since commercial operations began exactly three decades ago.

“We have improved the process as we have gone along, but the basics are the same,” says Grala.

From the lip of the on-site quarry pit, a crucible of rejected molten iron is poured down into a shallow pit. The glowing, lava-like flow bellows steam and bright orange clouds of iron oxide.

As each flow cools and solidifies, another lot is poured over the top until the shallow pit is full. The cold and layered iron is then broken up by a steel ball dropped from a crane, picked up by a magnet and trucked back a short way to the foundry to be recycled.

SteelServ is a company that specialises in metal recovery and providing steel works services. Owned evenly between the Multiserv Group and Glenbrook Steel Works, the company operates all the iron recovery operations at the mill site. Last year SteelServ was also commissioned to quarry old 12 tonne iron or steel castings (called skulls) from around the mill site that had been discarded and buried in the past because of imperfections in the castings.

As the price of scrap iron soars, steel mills around the world have been retrieving their skulls and breaking them up into more manageable one tonne pieces for recycling in steelmaking furnaces.

Over three decades of steel making, Glenbrook’s ‘backyard’ became full of skulls and other rejected iron castings. The recovery operation started in May 2007 and was completed by the end of the year, thanks to a demanding 22-hour, two-shift, on-site skull-busting operation.

“The skull recovery operation produced close to 50,000 tonnes of valuable scrap iron,” says Grala. “Most of the recovered iron has now been retrieved and processed. There’s a few skulls left and, bit by bit, we will process them over the next couple of years.”

The skull busting pit looks more of a war zone than a processing plant, and is surrounded by containers to protect the mill site from the steel shrapnel that can fly off the broken skulls with the force of a canon ball.

It is standard practice to smash the skulls with a 12 tonne steel ball dropped from the end of a crane boom and a deep field magnet. This fracturing also breaks off the outer layer of high silica slag covering the skulls. To speed up cycle times, SteelServ commissioned a 75 tonne excavator with a grapple hook (designed by Award Attachments) that could pick up a 12 tonne steel ball and drop it from a height of 15 metres.

“The magnet and the grapple both have pros and cons during the process,” says Grala. “The magnet and ball is easier to use and has less moving parts so required less servicing and down time. Processing times using the grapple and ball are quicker, as you don’t need the support of a front end loader to line up skulls – this can be done by the grapple.”

While the skull bashing has slowed down, the ‘pour on the ground and retrieve’ quarry operation continues as standard practice, says Grala, a South African trained mechanical engineer.

“Traditionally in a steel works about 15 percent of steel is rejected and recycled.”

Grala has worked at the mill for the past 21 years, after arriving from South Africa where he also worked in the steel works industry. Apart from the metal recovery process, there are aspects of Glenbrook that are unique, he says.

“We only use iron sands to make our iron and steel.”

This iron sand comes from the Waikato North Head mine site and concentration plant, located 18 kilometres south of the mill, close to the mouth of the Waikato River. The sand is initially concentrated using double drum magnetic separators, cleaned and stockpiled.

The concentrate is mixed with water to produce a slurry, for ease of transport, and then pumped from the Waikato North Head plant through an 18-kilometre underground pipeline to the Glenbrook steel mill.

Waikato North Head has more than one billion tonnes of iron sand reserves that contain at least 33.8 percent titanomagnetite, the main iron mineral in the sand, with reserves estimated at 74 million tonnes. These will yield 19.4 million tonnes of concentrate containing 59 percent iron. Around 70 percent of the processed sand is returned to the mined area, where it is re-contoured into dunes and planted in pine forest.

The recycling theme continues through the process, comments Grala.

“Iron and steel are the ultimate recycled material. Nothing goes to waste.”