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Case Studies - Burnt Lime

Hiway Stabilizers and Graymont

Product Sector: Industrial-Roading and Construction

Location: Silverdale, Auckland

Products: Burnt Lime and Hydrated Lime

Source/ Interviewee - Hiway Stabilizers

  • Graeme Quick fall, Business Development Manager
  • Mike Nelson, Operations Manager
     

Introducing Hiway Stabilizers

  • Hiway Stabilizers are New Zealand’s leading stabilisation specialists – with a company philosophy of sustainable civil engineering.
  • The stabilisation process involves modifying and strengthening existing clay materials for use in roading and construction projects – rather than using new materials to form a project base.
  • By avoiding costly and wasteful dumping of existing base materials, stabilisation offers significant economic, engineering and environmental benefits.

The challenge: getting lime in the right quantities, at the right time

  • According to Hiway’s Operations Manager, Mike Nelson, being able to respond quickly to project demands – where and when needed – is all in a day’s work.
  • “As a contractor, we need to be ready to go when the client wants and the weather demands. Also our volumes can be all over the place – because what we need varies depending on the weather, and the client’s general programme. The key thing we need from our lime supplier is the right volume, in the right location.”


Why Graymont?

Continuity of supply and delivery

  • Hiway uses a range of lime products. Calcium oxide (from 3mm minus to large clean chip) and hydrated lime is used in conjunction with specialised equipment, including computer controlled stabilising machines and piling rigs.
  • Having a ready supply of product, available in any volume, is critical to Hiway.
  • “McDonald’s (now Graymont) are by far the most significant lime supplier and can supply large quantities of product at short notice,” says Mike. “And their cartage contractors are excellent – they’re very reliable and provide exceptional service.”

Collaborative relationship

“We have a very collaborative relationship with McDonald’s (now Graymont),” says Mike Nelson. “We need them to be hugely flexible, and they are. They’re willing to increase storage and delivery capacity to meet demand – and that’s even meant providing additional onsite storage for some of the bigger jobs we’ve had to complete within tight timeframes in the past.”

Long association

  • Hiway Stabilizers was one of the first companies to pioneer the stabilising process in New Zealand more than 25 years ago, and McDonald’s Lime (now Graymont) has been their partner from the start.
  • “We’ve been dealing with McDonald’s Lime (now Graymont) since the early 1980s,” says Mike Nelson. “Quite simply, they deliver exactly what we need, when we need it.”

Oceana Gold

Case Study: Lime and Mining

Product Sector: Industrial-Mining       

Location: Macraes Goldfield, Otago               

Product: Burnt Lime

Source/ Interviewee - Oceana Gold 

  • Andrew Cranely, Metallurgical Superintendent

 

Introducing Macraes Mine

  • Macraes Gold Mine is New Zealand’s largest gold-producing operation, producing more than two million ounces of gold since current mining operations began in 1990.
  • Located in the historic Macraes Goldfield, about 100km north of Dunedin, the operation consists of a large-scale open cut mine and underground pit with an adjacent processing plant.
  • Macraes Mine is owned by OceanaGold Corporation, a Pacific Rim gold producer which has a diverse portfolio of operation, development and exploration assets.

The challenge: recovering gold cost-effectively and boosting efficiency

  • The challenge for Macraes is to meet the special requirements of extracting gold at the mine.
  • Because the ore at Macraes is naturally resistant to the usual recovery process of cyanidation and carbon absorption, they need to use an autoclave machine.
  • “Use of an autoclave is a bit unusual,” explains Macraes’ Metallurgical Superintendent Andrew Cranley. “The autoclave operates at high temperatures and pressures to help make the gold more available.”
  • Taylor’s (now Graymont) lime is used to modify the pH in the process. Calcium carbonate chips of 2mm are used in the autoclave to control free acid created in the treatment process.
  • Lime oxide is also used as a carbon modifier in sections of the plant where the gold is dissolved out of the ore and then recovered onto carbon.

Why Graymont (formerly Taylor's Lime)?

  • Good service

“At Macraes we place a big emphasis on service – and the quality of Taylor’s (Graymont) service stands out,” says Andrew. “Taylor’s (Graymont) are certainly proactive. They come to our site regularly to see what they can do to help. We have a good relationship and the service is quite personal.”

  • Continuity and quality of supply

“Our consumption rates are sometimes quite a bit higher than budget – at times they are 100% higher. But Taylor’s (Graymont) have always been able to supply, and they are nowhere near full utilisation of their quarry.” The two companies keep in on-going communication regarding supply. Macraes send down silo readings to make sure the silos are always full enough for production requirements. “Taylor’s (Graymont) work in closely with us to make sure that we have enough product in stock.”

  • Collaboration

“Our relationship is an open two-way street,” says Andrew. “For instance, recently we had an autoclave shut down, and we were emptying the lime mixing tanks for servicing. Taylor’s (Graymont) were able to provide us with a temporary lime mixer so that we still had a supply of lime over the maintenance period.” The two companies also collaborate in other ways. “We’re also working with one another on health and safety; by getting our staff to visit each other’s sites and sharing information.”

  • Overall

“We are always monitoring performance – identifying ways to improve performance, extract more ounces and reduce costs. We find that Taylor’s (Graymont) are always evolving and improving their product and service too.”

NZ Steel

Case Study: Lime and Steel Production

Product Sector: Industrial-Steel Production

Location: Glenbrook Steel Mill, New Zealand

Products: Burnt Lime, Limestone Chip and Hydrated Lime

Source/ Interviewee: New Zealand Steel-Connal Holmes, Principal Technologist, Steelmaking

 

Introducing New Zealand Steel

  • New Zealand Steel Limited is NZ’s sole producer of flat rolled steel products for the construction, manufacturing and agricultural industries
  • Using locally-sourced iron sand, NZ Steel produces around 620,000 tonnes of steel each year
  • The company is committed to being a world-class steelmaker, and exports about 60% of its steel output

The challenge: Securing top grade lime products to produce top grade steel

  • New Zealand Steel operates a fully-integrated steel mill at Glenbrook, about 60 kilometres south of Auckland
  • Crushed burnt lime transferred by pneumatic line of the steelmaking furnace, to generate slag to remove impurities from the steel
  • According to NZ Steel’s Principal Technologist, Steelmaking, Connal Holmes: “We need a very high grade limestone to produce the burnt lime – we can not have excessive levels of impurities like silica, which would cause wear on our transfer system.” The other specific requirement is the size of the lime; it cannot be larger than 1mm or it will not fluidise and inject via the tuyere [or nozzle] to the furnace interior. “We also use lump burnt lime at the ladle treatment station to create the slag that we want. We add limestone chip to the furnace as a coolant, and we use hydrated lime as a water treatment for pH control.”

Why Graymont?

  • Product quality/quality control

Graymont carries out routine chemical analysis and sizing checks to ensure that finely ground calcium oxide is supplied within tight standards that is required by New Zealand Steel.

  • A great relationship

“We have good communication and a very open way of talking with McDonald’s (now Graymont) . We have regular meetings, plant familiarisation visits to each other's operations and very few issues" says Connal. 

  • Long association

The two businesses share a long history.When McDonald’s relocated to the Waikato in the 1960s, it coincided with the opening of the Glenbrook mill.
“We’ve worked with McDonald’s ever since both our businesses began in the 1960s,” says Connal. “It’s a mutually beneficial relationship.”