Fly ash: waste not, want not

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 24 Jul 2012   Posted by admin


A recent World Trade Organization ruling established that China – which produces nearly 90 per cent of the world’s supply of magnesium – was violating a number of international trade obligations pertaining to its minor metals policies.
Magnesium, which is 40 per cent lighter than aluminium and as strong as steel, is a critical element in the manufacture of energy-efficient cars, lightweight laptops, mobile phones and other electronic devices. Moving to fill a widening rift between increasing demand and constricting supply, Latrobe Magnesium (LMG) has been
working towards the development of a magnesium production plant in Victoria’s Latrobe Valley that will use an innovative, world-first combined hydrometallurgical (hydromet) and thermal reduction process.
The magnesium plant will extract magnesium from industrial fly ash: a natural waste product of brown coal power generation. Construction of the plant is expected to begin in March 2013, with first production, intended solely for the domestic market, due a year later. LMG has outlined plans to expand supply for offshore users once
the profitability of the project has been established.
Latrobe Valley, which boasts brown coal reserves that could power Victoria for another 500 years at existing consumption rates, is the heart of the state’s coal power generation area – perfectly positioning LMG with direct and constant access to magnesium-rich fly ash.
Home to all of Victoria’s major power plants, including Hazelwood, Yallourn and Loy Yang, the Valley accounts for about 85 per cent of the state’s power generation.
This has resulted in large quantities of discarded fly ash: a resource of more than 25 million tonnes to which a further 500,000t is added each year.
Environmental benefits
In the Latrobe Valley, an area infamous for its mammoth carbon emissions, LMG has committed the company to the highest environmental standards: culminating in a project that is both economically-and environmentallysustainable.
As the LMG plant will be in close proximity to existing power stations, the feedstock can be transported directly into the plant via a slurry pipeline – reducing the economic and environmental effects of the trucking alternative.
Unlike many magnesium plants that use a magnesium carbonate feedstock, LMG only uses fly ash, which contains magnesium in a mineral oxide form. As a result, minimal carbon dioxide will be produced during processing.
While the environment in the power stations’ fly ash disposal areas has already been seriously affected, the LMG project aims to rehabilitate the fly ash- affected areas and upgrade the surrounds, thereby improving the landscape and visual appeal of the area.
LMG has estimated that its process will remove up to 75 per cent of the fly ash produced by a power station, while water from the fly ash slurry will be recycled back to the power stations for reuse.
On the road to production
The hydromet process developed by LMG in conjunction with Australia-based consultancy Ecoengineers involves the low-cost, high-return treatment of fly ash to reduce sulfur, iron and silicon to suitable levels so the beneficiated material can be used as a feedstock in the ensuing thermal reduction process.
A worldwide patent application for the hydromet process was lodged in August 2011 by Ecoengineers and LMG, who jointly own the worldwide marketing rights for this technology, to protect their intellectual property.
LMG released its pre-feasibility study on the project in October 2011, with the company subsequently announcing in December of that year that initial gravity separation tests had achieved up to 32 per cent iron removal from the magnesium. LMG has since achieved up to 55 per cent iron removal using its hydromet process. Increased iron removal leads to lower operating costs along with better feedstock and magnesium recoveries in the thermal reduction process.
Confident of the results, the LMG board immediately moved to allow the company to progress towards a bankable feasibility study.
However, the pre-feasibility study brought to light a number of smaller issues that needed investigation, including the validation of some of the hydromet process assumptions that were used in the study, which have since been dealt with as part of a four-part test work program. LMG conducted optimisation tests to refine the hydromet process as part of program one in January 2012. This program focussed on the desulfation step of magnesium production, and the company reported that a shorter reaction time combined with less reagent usage could be achieved, reducing capital costs in the step by four times than estimated in the pre-feasibility and reducing overall operational costs.
Program two, started mid-March, sought to produce significant quantities of material for additional thermal reduction process work as well as cementing property test work.
Designed to investigate some process improvements, these program two tests were completed by the end of May.
Program three will focus on processing Yallourn fly ash using the hydromet process. Initial x-ray fluorescence (XRF) and x-ray diffraction (XRD) analysis of this fly ash has been undertaken, revealing that it contains a higher iron content than Hazelwood fly ash, but with magnesium at acceptable levels. The detailed hydromet test work
started in early April and is due for completion in June.
Program four will focus on processing large German electricity supplier RWE Power AG fly ash using the hydromet process. Initial XRF andXRD analysis that has been conducted simultaneously with the Yallourn program has revealed that the ash should be suitable for treatment by the hydromet process.
In a move that further underlined the economic and environmental viability of the project, LMG signed a confidentiality agreement with Holcim Support Group on March 12 to investigate whether the cementious material produced as a by-product of the LMG hydromet process would be suitable for use in the manufacture of
portland cement.
As the chemistry of the cementious material produced from Latrobe Valley brown coal fly ash is similar to portland cement, LMG is undertaking further test work.
On May 1, LMG signed a co-operation agreement with Beijing Tieforce Engineering (BTE) to assist with the former’s smelter project. BTE has secured approval from the Chinese Magnesium Association to enter into the agreement and has significant experience in the construction of thermal magnesium plants in China.
It also designed and constructed the 15,000 tonne per annum Perak magnesium smelter that was fully commissioned in Malaysia in 2011. BTE will test LMG beneficiated fly ash in both a laboratory and a commercial facility to determine the main technical requirements and performance indices for the construction of the new magnesium plant.
International interest
In October 2011, LMG signed a confidentiality agreement with RWE to investigate whether the LMG hydromet process was suitable to process brown coal fly ash in Germany.
LMG has subsequently identified one RWE brown coal mine near Cologne that produces about 100 million wet tonnes of coal per annum, and which believes has magnesium-rich fly ash comparable to Hazelwood.
LMG believes that if the fly ash is suitable, this mine may have the capacity to produce more than 36,000t of magnesium.

 

By Reuben Adams


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