The concentrate storage dome at Sierra Gorda, designed and built by Geometrica.
Keeping Concentrate Shipments
Under Control
Moving metal concentrates from mine to market can present some operational
challenges, especially from an environmental perspective
By Simon Walker, European Editor
In essence, the requirement is for concentrates to be moved efficiently from mine to port by road, rail or (rarely) pipeline, and then from port to smelter by ship. At each stage of the operation, materials- handling systems are needed that can cope with high-density, finely ground material, while both mines and ports require dedicated storage facilities that can provide both security and physical protection from wind and rain.
Tighter environmental regulations covering the movement of concentrates have also resulted in a major upgrading of the transport systems used, with open-topped trucks or rail wagons having been superseded by soft, tarp-type covers initially and, more recently, by hard-top covers and specially designed transport containers. The reduction achieved in dust emissions has, of course, had another advantage in that producers are losing less from their bottom line as transport systems become more secure.
Port Regulations Tighten
One of the first events that seems to have
triggered increased public awareness of
the potential for environmental impacts
from concentrate transport occurred at
the Western Australian (WA) port of Esperance
in 2007.
As described in a case study from The International Lead Association, early that year reports began emerging of unusual numbers of bird deaths in the area around the port, through which concentrates were being shipped from Magellan Metals’ lead carbonate mine near Wiluna, and from various nickel mines in the state.
Up to then the concentrate had been transported in bulk from the mine in tarpaulin- covered containers by truck and train, before being stockpiled at the port inside a large shed awaiting loading into ships by a series of conveyors. Investigations revealed high levels of lead and nickel around the port and its community, with inadequate infrastructure and the mishandling of the lead carbonate concentrate during bulk loading onto ships in hot, dry and windy conditions having allowed lead dust to escape.
The WA state government subsequently banned the export of bulk lead carbonate from the port, effectively blocking off Magellan’s exporting route and forcing the company to place its mine on care-and-maintenance until an alternative transport system had been approved. At that time, some 8,000 metric tons (mt) of concentrates remained in storage at the port, with a further 22,000 mt awaiting transport from the mine.
Magellan — subsequently renamed Rosslyn Hill Mining and a subsidiary of LeadFX — devised a system using 2 mt-capacity double-lined bulk bags that were filled at the mine, vacuumed on their exteriors and placed inside steel shipping containers, which were then locked and washed. After a 400 km road journey to Leonora, the containers were then loaded onto rail wagons for the 850 km journey to the port of Fremantle for export.
A similar system was used to remove the concentrates remaining at Esperance, with all of the material being cleared from the storage area by mid-2009. The stockpile at the renamed Paroo Station mine was also shipped out, although the mine itself — having been restarted in 2013 — was again placed on care-and-maintenance two years later in response to depressed lead prices.
In December, LeadFX announced that it has received a seven-year extension for access to the port of Fremantle to export its concentrates. This, it noted, was a critical step in its preparations for a potential restart at Paroo Station — which will depend on both improved lead prices and the securing of restart funding.
While acknowledging that lead presents specific environmental challenges throughout the production and transport cycle, the impact of the Esperance incident has been felt much more widely within the concentrate-shipping business. With fugitive dust emissions from all types of industrial operations increasingly being targeted as sources of public annoyance at best, and as contaminants at worst, concentrate producers, transporters and port operators have been investing in new infrastructure and systems that provide better security and emission control for all types of mineral products.
Looking at Latin America
Ports handling concentrate exports in
both Chile and Peru have been investing
in new storage and materials-handling
facilities, as the requirements made by
both regulators and customers have been
increasing as regards both dust emissions
and product security.
For example, the port of Arica in far northern Chile handles concentrate shipments that originate in both Chile and Bolivia. The material arrives by train and road, with past practice having involved the open-air storage of concentrates in an area close to the harbor. Not surprisingly, dust emissions resulted in widespread metal contamination of the port and surrounding communities.
Over an eight-year period from 2005, the port management company invested some $9 million building sealed storage areas for concentrates, in addition to installing new conveying systems and improving the road surfaces. The result has been a marked reduction in emissions, with the port subsequently being awarded several accreditations for environmental compliance and energy usage reductions.
Speaking at the ceremony to inaugurate the $163 million facility, Ricardo Trovarelli Vecchio, chairman of Transportadora Callao, said: “Today we are inaugurating the most innovative terminal facility for loading mineral concentrates in Peru; this milestone positions Peru as a global leader in specialized infrastructure for the modern-day mining industry, a key economic and social driver for this country.”
Innovative loading processes provide quicker transport and ease congestion along the container port access routes, as well as cutting 130,000 truck journeys a year between the concentrate storage areas and the port itself, which helps to improve air quality. With an initial capacity of 3.7 million metric tons per year (mt/y), concentrate throughput is expected to rise to 6 million mt/y by 2034.
The construction project took 22 months and involved the installation of 3.5 km of conveyors, an access bridge, a dock and a shiploader. Throughput has been increased five-fold to 2,000 mt/h, while the cut in loading times, from typically eight days to a matter of hours, is estimated to save some $20,000 per ship per day.
Not content with that, Trafigura was later reported to be evaluating a $200 million investment in a new 2.6 million mt/y concentrate-handling unit at the port of Salaverry in northern Peru, with the aim of providing export facilities for copper operations such as Milpo’s Magistral project, Rio Alto Mining’s La Arena expansion and Newmont’s Minas Conga project.
And improvements to concentrate handling facilities are not only happening at ports. In addition to the Chilean projects described in the July 2016 edition of E&MJ (pp.38-43), US-based Geometrica built two enclosed storage domes at KGHM International’s Sierra Gorda copper- moly mine in Chile, opened in 2014. With a diameter of 122 m (400 ft.), the larger unit covers the coarse ore stockpile, while the concentrate storage dome spans 62 m (203 ft.) and has internal cladding to protect the galvanized steel structure from any possible corrosion from the moist concentrate.
As an example, concentrates produced at Teck’s Red Dog mine in Alaska are moved by truck the 83 km (52 miles) from the site to the port, with an average of 50 trips a day each carrying 85 mt of material in two specially designed side-dump trailers. Storage facilities at the port itself can hold up to 850,000 mt of concentrates, which are shipped out during what is typically a 100-day ice-free period from June to September. As well as the haulage trailers being covered, the port materials-handling system — including conveyors, the shiploaders and transfer barges — is also enclosed to prevent dust emissions.
In Australia, meanwhile, remote mines use the road-train system for transporting concentrates, with a single tractor unit towing (usually) two or three trailers. For instance, Glencore’s McArthur River mine in the Northern Territory uses haulage units consisting of two quad-axle side-tipping covered trailers with a payload of around 120 mt. These run on a 120 km (75 mile) journey from the mine to its port at Bing Bong, which has 60,000 mt of storage capacity and a dedicated barge to transfer the concentrates to vessels lying offshore.
Glencore notes that its approach to minimizing dust emissions from the road trains includes wheel washes at the mine and port, protective covers over each trailer, 85 km/h speed limiters on the vehicles, a fully covered unloading dock at Bing Bong, and specific tipping procedures at the storage shed to prevent any spillage.
Elsewhere in Australia, Glencore uses rail wagons to transport concentrates from Mt Isa to its export facilities at Townsville on the eastern Queensland coast. Covered wagons are unloaded inside a fully sealed shed, using a rotary tippler, with any dust generated being captured in filtration units. Opened in 2015 at a cost of some A$85 million, the facility’s conveyors and shiploader are also enclosed, with the company having spent nearly A$16 million on environmental improvements at the port since 2010 and a further A$17 million being budgeted for further enhancements.
Flexible intermediate bulk containers, to give big bags their official name, offer a low-cost solution for concentrate transport, with the advantages of weight consistency and ease of handling using forklifts or telehandlers. Readily available worldwide, FIBCs are also lightweight when empty and are easy to store, providing containment to the material inside. Their downside, of course, is that they are still open at the top when filled, so the potential for spillage or wind erosion of the contents remains and they are perhaps better used for materials that are relatively inert — such as industrial minerals or mineral sands.
Taking containerization a stage larger, the Australian company, Intermodal Solutions Group (ISG), offers open-top and sealed containers designed specifically for handling direct-shipping ores and mineral concentrates. One example of its range is its 20 ft. copper concentrate container, which has a capacity of 20.5 m3 and a payload of just over 30 mt. Made of steel with a tare weight of just 3.45 mt, the container is designed to be compatible with all tipplers in the Australian market, and includes a lid that is automatically locked and unlocked by the tipplers. The company has produced 1,400 of these units for OZ Minerals, which are used for transporting copper concentrate from the Prominent Hill mine in South Australia to the port of Adelaide.
Other containers in ISG’s ‘Pit-to-Ship’ range include a 20 ft. unit designed for handling nickel concentrates, and a 20- ft. half-height unit for iron ore, as well as those designed for handling bulk coal, fitted with tarpaulin covers.
And the company does not only supply the domestic Australian market. Overseas, ISG has won orders from Codelco for copper concentrate containers, from Exxaro for 1,350 iron-ore containers for an operation in the Congo Republic, and from MMG for 1,200 copper concentrate units for its Las Bambas mine in Peru.
The Las Bambas concentrate-handling project, which won the innovative technology award from International Bulk Journal last year, involves transporting 1.4 million mt/y of concentrates 443 km by road to the nearest railhead, then a further 286 km to the port of Matarani for export. The 17.5 mt-capacity ISG containers are designed to fit two per truck and three per rail wagon in order to meet local weight restrictions.
Empty containers arriving at the mine have their lids removed before being filled by wheel loaders, after which the truck wheels are washed, the container rims vacuumed and the lids refitted. Trucks are then sent in convoys to the rail transfer station, where the containers are lifted on to wagons, each train carrying 54 containers.
At the port, loading from the containers directly into ships or into the storage area is achieved using two bridge cranes equipped with RAM Revolver spreaders, which lift each container from its wagon, remove the lid and gently rotate it so that the concentrate is tipped out.
According to RAM, the end result is that MMG successfully implemented an innovative bimodal truck-rail transport solution, with direct loading from rail at the port with no need to re-handle containers or build additional infrastructure; the first of its kind in the world, the company claims.
Shipping Risks No matter how many precautions are taken, accidents will happen whether materials are being transported by road, rail or ship. Trucks carrying concentrates do overturn from time to time, either because of mechanical failure or driver error, and concentrate cargoes can be lost at sea in bad weather or through the mechanism of liquefaction.
Richard Brough, technical adviser to the International Cargo Handling Co-ordination Association (ICHCA), commented: “The tragic loss of the Bulk Jupiter, which sank off the coast of Vietnam in 2015 carrying a 46,000 mt cargo of bauxite, highlights the need for all those involved in the supply chain to take responsibility in assessing the solidity of bulk cargoes.”
According to a study by Mathias Grote and co-authors, published last year in Marine Pollution Bulletin, at least 23 ships lost at sea during the period 1978 to 2012 were carrying mineral concentrate cargoes that were potentially hazardous to the marine environment. Their admittedly incomplete research suggested that during the period, nearly 300,000 mt of copper concentrates had been involved, nearly the same tonnage of nickel ore and around 55,000 mt of lead concentrates. Their figures do not include commodities such as iron ore or coal, with bulk carriers of both having been lost as well.
With the exception of the Jambo incident (described in the sidebar on p. 28), it is rare indeed for any recovery of concentrates from sunken ships to be possible. Conversely, clean-up operations are invariably needed when trucks or rail wagons overturn, although the quantities involved are, of course, an order of magnitude less.
Without doubt, mining companies, transport firms and port operators are all now better equipped than ever before to handle what are, after all, highly valuable concentrate shipments. Environment and bottom-line benefits are being achieved, with success in reducing emissions from concentrate handling helping the longterm goal of enhancing public perceptions of mining.
Case Study: Recovering Sunken Zinc Concentrates
While most of the mineral cargoes lost at
sea sink to depths well beyond practical
or economic salvage, an exception — witnessed
by this author — occurred in June
2003 when a vessel carrying some 3,300
metric tons (mt) of zinc sulphide concentrates
from the Tara mine in Ireland
was wrecked on an island off the remote
northwest coast of Scotland. The ship,
the Jambo, had loaded in Dublin and was
heading towards the Odda zinc refinery
in Norway when it veered off course and
hit Eilean Fada Mòr in the early morning
of June 29th. Having grounded, it took
on water and subsequently sank, coming
to rest with its bow exposed and its
stern at a depth of around 30 m (100
ft.). The subsequent enquiry determined
that crew fatigue was the principal cause
of the accident.
The near-pristine waters off northwestern Scotland host an important local fishing industry, with initial concerns over the impact that concentrate leaching might have on local fish and shellfish stocks. With the ship’s fuel load recovered, the U.K. government entered into an agreement with the Protection and Indemnity (P&I) Club that had underwritten the Jambo’s insurance, agreeing to underwrite 50% of the cost of recovering the cargo.
Beginning in July 2003, the operation continued until mid-October, when the government’s agreement with the P&I Club expired. By that time, Smit had recovered around 1,900 mt of concentrate, with the remainder effectively lost on the seabed. Major obstacles to the operation had included zero visibility for the divers working in the hold, the density of the finely ground concentrate — which caused it to resettle quickly before the pumps could suck it to surface — and the long settling time needed in the barges before surplus water could be decanted overboard and more slurry loaded.
Weather systems rolling in from the Atlantic also caused delays, so what was originally intended to be a two-week operation extended to nearer 10. And while the operation marked a major change in political will towards minimizing the potential impact of mining and its products on the environment, this was a rare instance where circumstances allowed recovery to take place.
As it happens, long-term monitoring has indicated that the residual cargo has had no significant effect on marine life in the area, and the wreck — now completely submerged and overturned — is a popular amateur dive venue for those hardy enough to brave the frigid Scottish sea.