Characterization and Assessment of Iron Ore Tailings as Raw Materials for Construction Industries

Introduction

Iron is one of the world's most commonly used metal derived from iron ore. Iron is the key ingredient, representing almost 95% of all metals used per year (U.S. Geological Survey [USGS], 2017). It is used primarily in structural engineering applications, maritime structures, automobiles, general industrial machineries and equipment, etc.

World production of iron ore was more than two billion metric tonnes of raw ore annually. China is by far the largest producer, consumer, and importer of iron ore. In 2015 alone China produced 1.3 billion tonnes of iron ore equivalent to 44% of the world’s output. Australia comes as the second largest producer of iron ore that produced 824 million tonnes in 2015 representing more than 20% of the global output. Brazil is the third largest producer of iron ore producing 751 and 411 million tonnes in 2015 and 2014, respectively. Brazil’s 2015 output represented 12% of the world’s production. In the past, India was a world leader, but now stands the fourth largest producer. In 2015, India produced 129 million tonnes of iron ore. Russia is the fifth largest producer, and in 2015 it produced 112 million tonnes of crude iron ore.

Iron ore tailings (IOT) are waste materials generated when iron ore is processed by separating valuable fractions from the worthless ore. Enormous quantities of industrial wastes produced from mining industries are usually disposed of to landfills due to uneconomic attractive usage. The continuous disposal of IOT endures over-burden to the mining industries and the community in terms of environmental and economic perspectives. For instance, in China the total stockpiles of iron ore tailings was 2.899 billion metric tonnes during the years between 2007 and 2011. Of that, approximately 806 million metric tonnes were generated in 2011. However, only 307 million metric tonnes of tailings were comprehensively recycled (Cai et al., 2016). Goyal et al. (2015) reported that approximately 10 – 12 million tonnes of such mined ores are lost as tailings in India. In Europe, about 2.75 billion tonnes of mining waste have been produced between 1998 and 2001 (Grangeia et al., 2011). The estimated iron ore production in Brazil for 2015 was 751 million tonnes and generated 260 million tons of iron-ore tailings (Carrasco et al., 2017). The increased accumulation of iron ore tailings and eventually their disposal pose an over-burden to the mining industries and the community in terms of environmental and economic perspective (Zhang et al., 2006). Lack of space for the disposal of huge amount of IOT stocked in the industry will become a major problem in the future. There are other possible issues, such as, leaching of heavy metals and acid mine drainage which could cause havoc to the community and the environment (Hitch et al., 2010).

As mentioned earlier, IOT stockpiled in the tailing dams might be risky to the environment and the impacts could be physical, chemical or geotechnical instability. The possible effects for storing the tailings in the dam could lead to soil and surface water pollution due to toxic substances such as lead, sulphates and dissolved metals. Sulphates, in particular are susceptible to chemical oxidation when exposed to oxygen and form acid in the soil. In this case the acid might possibly kill vegetation and diffuse into ground water.

The persistent disposal of IOT in landfills or tailing dams has a range of environmental issues, which include: erosion, dust, water and soil pollution, negative effects on the ecosystems and loss of land fertility. The difficult situations that might be encountered are during the failure of tailing dams or collapse of heaps due to earthquakes and heavy rainfall, which could affect the environment and health safety of human life (Cai et al., 2011).

In order to find a solution for the environmental issues raised and sustainability of natural resources, there is certainly a need to further study the characterization and microstructure of the waste material that will increase the percentage of tailings utilization as construction and building materials. Current utilization of IOT at 7 to 10% (Zhao et al., 2014; Huang et al., 2013b) is very low compared to huge disposal ranging from 5 to 7 billion tonnes per year worldwide (Edraki et al., 2014). Increasing the utilization of IOT will provide eco-friendly, economic and environmentally sustainable mining industries and also provide alternative and cheaper building and construction materials.