Making good use of cement kiln dust

 

Holcim New Zealand has utilised technological developments driven by environmental awareness and product stewardship objectives to create a new environmentally beneficial process for the mining industry. Cement Kiln Dust (CKD) is a by-product of cement production that is now being used to produce controlled low strength fill (CLSF) for Solid Energy’s Stockton mine void stowing program. Coupled with the use of the alkali CKD in engineered capping for acid mine drainage management, the most environmental appropriate solution has been achieved.

CKD is generated when cement clinker is produced in Holcim cement works kilns. Holcim has employed the most environmentally appropriate management process available for CKD since production started at Westport in 1958. Initially the dust was sent to controlled landfill and stockpiles. Holcim has continually sought to utilise this by-product in various ways as well as reducing its generation.

Waste hierarchy indicates the evolution of industrial by-product management from disposal to prevention.

 

Harvey Tyler, Technical Sales Manager for Holcim New Zealand, highlights the environmental benefits of this product development. "Not only are we taking a significant amount of material out of the waste stream, the use of CKD in coal mining is bringing environmental benefits, coal mining efficiencies and site safety benefits to that industry," said Harvey. " Significant effort and work has been conducted in conjunction with Solid Energy over the last 18 months to achieved this mutually beneficial outcome that heralds a new age in the relationship between Solid Energy and Holcim" Harvey continues.

The Millerton Block located in the northern part of the Stockton Mine has 1.25 million cubic metres of underground voids as a result of historic underground mining methods. The use of CKD in creating CLSF, used to fill or stow the voids, is a success story for both Holcim and Solid Energy. Void stowage in areas which have been extensively mined can prevent heavy machinery falling into unseen voids, reduce acid drainage runoff and contributes in no minor way to extinguishing underground fires.

Big Yellow on the Stockton Mine plateau – 115 tonnes, 17 metres long, with a body made from 40mm steel plate.

 

Hardened CLSF extracted via opencast methods, with inherent alkaline properties from the CKD, is used in engineered caps for management of acid mine drainage. There are a number of other practical benefits. Void stowing also results in improved opencast coal yields with waste minimisation of the excavated.

CLSF is easily applied by the mobile mixing and processing plant, known as ‘Big Yellow’ that is track-mounted and loads the dry mixed CLSF. It travels to boreholes to gravity flume fill the voids below ground. Holcim’s research and experience in Australia at the Blair Athol Mine has demonstrated the need for tight control of the mix water, raw material blending and fluming of the CLSF to achieve required performance outcomes of targeted strength development, tight filling of voids and preventing segregation

The hardened CLSF after opencast excavation showing tight filling of the void.

 

The hardened CLSF after opencast excavation showing tight filling of the void.

The West Coast Regional Council has embraced the use of CKD both as an acid mine drainage management tool and in CLSF for void stowing. The use of CKD in engineered caps and in CLSF has shown to be an effective tool in achieving superior environmental outcomes for mine management.

According to Jason Greig, Opencast Commercial Manager for Solid Energy, "The use of CKD in void stowing and in engineered caps has been a vital part in developing a workable and viable opencast mining plan for the area".

Stockton Alliance is on target to complete 95,000 m3 of void stowing this financial year with projections of tripling this amount of stowing in 2012 with the commissioning of Big Yellow.

The industrial by-product CKD from cement production has evolved from a waste disposed to landfill to a valuable reusable constituent in a mining application with numerous safety, environmental quality and waste minimisation benefits. The CKD waste resource increases in usefulness with decreasing environmental impact.

For further information please contact Harvey Tyler, Technical Sales Manager – Cement, 03-3397575 or harvey.tyler@holcim.com