Tailings and related waste

The National Weekender
ENVIRONMENT

By GODFRIED ANGI
THIS article is the continuation of my last article on mine tailings.
Before proceeding into details of tailings let us take a look at how mines are developed, from exploration to the end of a mine’s lifespan.
Mining for gold, copper, nickel or any other mineral and oil and gas development activities encompasses any number of activities relating to the development and operation of the mine. All these activities relate to the generation of a variety of waste streams. There are four main phases of mine development and operation: Exploration, mine development, mining and milling, smelting and refining.
In oil and gas it involves exploration, drilling, processing and refining. Each of these phases of development and operation involves habitual changes to the existing environment.
Exploration phase or preparatory works – The preparatory works during the exploration activities involve a number of activities in the field which often precede feasibility studies, initial reconnaissance flights and geophysical surveys, stream sediment studies and other geochemical surveys, construction of access roads, clearing of test drilling sites, installation of drill pads and drilling rigs, benching, trenching/pitting, erection of temporary accommodations, and power generation for exploratory drilling.
Wastes generated during this phase include exccess soil and rocks (overburden), wood debris, hydrocarbon wastes, metal parts and domestic wastes.
Mining development or construction phase – The development of a mine has implications such as overburden stripping and placing; drilling and trenching; road/trail, building and/or helicopter transport; erection of treatment plants, preparation of disposal areas, and construction of service infrastructure such as staff accommodation, office buildings, ore processing plants, power line or generating plants, water supplies, sewerage treatment facilities, laboratories and amenities.
The wastes generated during this phase include overburden, wood debris, hydrocarbon wastes, metals and domestic wastes.
Mining and milling or operational phase – Mining and milling may include the following:

  • Feasibility, engineering design and environmental impact assessment studies;
  • Mine construction and pre-production – underground mining, surface mining in open pits or placer deposits and can include hydraulic mining in or near riverbeds;
  • Stripping/storing soil and vegetation overburden;
  • Ore extraction;
  • Crushing or grinding of ore;
  • Flotation or chemical concentration of ore;
  • Mine and surface water treatment; and
  • Storage of waste rock and tailings.

Tailings are generated during ore processing in the Ore processing plants where certain chemicals are applied in extracting gold. Potential environmental impacts on mining and milling include:

  • Wildlife habitat fisheries loss
  • Changes in local water balance
  • Increased erosion and sedimentation of lakes and streams
  • Containment of toxins in tailings ponds or leaching solutions
  • Tailings ponds or leaching pads stability failure;
  • Potential acid generation from waste rock and pit walls
  • Heavy metal leaching from acid mine drainage
  • Cyanide solution containment at heap leach operations;
  • Containment of surface water and groundwater from discharge of acid mine drainage including heavy metals originating in ore and tailings, organic chemicals and cyanide originating from milling processes; and
  • Alienation of land as a result of waste rock piles and tailings disposal areas, and noise and wind-borne dust.

Smelting and Refining or Gold Processing – The smelting and refining phase may include activities such as subjecting minerals concentrate to high heat or electro-chemical process to form ingots or bars of pure metal or alloy. On-site processing may include a combination to reduce particle size, flotation using selected chemicals, gravity separation or magnetic, electrical or optical sorting, and ore leaching with a variety of chemical solutions. Associated transport storage of ore and concentrates may be a handling risk, which can result in localised site contamination. Potential environmental impacts on smelting and refining include:

  • Heavy metals, organics and sulphur dioxide emissions to air;
  • Discharges of toxic chemicals such as sulphuric acid and ammonia used during processing, and
  • Alienation of land as a result of the generation of slag and high energy consumption resulting in indirect environmental impacts.

Gold mining is a highly consumptive and environmentally destructive extractive industry. The industry destroys and reconfigures landscape together with its biota. Open pit gold mining creates massive amounts of toxic waste that often causes acid mine drainage and heavy metal contamination. The gold mining processing also uses large volumes of water and energy, often subsidised. It also utilises dangerous chemicals such as cyanide in its leaching processes, posing a threat to the biota of riverine ecosystems.
Acid mine drainage and water pollution
Leakage, leaching and draining of acid solutes is a major environmental problem facing mining industries. Open pit mining in particular, creates great waste for a small yield. On average, it takes some 79 tonnes of waste to extract one ounce of gold, according to a conservative estimate by EarthWorks and Oxfam (www.minewatch.com). The process involves grinding up ore, and then exposing it to cyanide in order to extract the gold. Sulfides in the crushed rocks interact with oxygen and water to create sulfuric acid, and together with the mobilisation of other contaminants, create acidic water (Mehta, 2002; Hudson, 2012). The acidic water is commonly called acid mine drainage (AMD) or acid rock drainage (ARD).
Acid drainage is generated at both abandoned and active mine sites (MINEO consortium, 2000). This acidic water is able to dissolves toxic metals, such as copper, aluminum, cadmium, arsenic, lead and mercury, from the surrounding rock. These metals, particularly iron, may coat the stream bottom with an orange-red colored slime called yellow boy (Environment Australia, 2002) or red river [wara] as dubbed in PNG. In and of itself, AMD is harmful to ecosystems because it makes water too acidic to support life (Ogola et. al. 2002).
Land degradation, deforestation and soil rrosion
Mining is a very destructive extractive industry. Gold mining involves both open-cut and underground operations. The ore is then crushed and panned and the waste rock is dumped into heaps as dumps or tailings. The mine will leave behind dredged out and contaminated streams, disturbed vegetation and littered landscapes, open trenches and pits filled with water. Land degradation is a common sight in abandoned mines (Ogola et al, 2002). Land degradation is due to AMD resulting from open-pit mine which are partly washed on to adjacent land.
Disposal of waste or tailings in rivers and creeks often raises river beds, facilitating overbank flooding that can destroy riverine forests as well as human settlements along banks. Destruction of forest will exacerbate soil erosion, leading to extra sediment loads input into rivers and creek (Ogola et al, 2002).
Options for rehabilitation of landscape in mining areas are not easy. Most miners are not landowners, thus they quickly abandon the degraded sites and move to new productive ones. The landowners are therefore left with wasteland.
Air pollution
Mining and dust are inseparable. Air pollution comes mainly from silicate dust from ore mining and crushing. The inhaling of this dust is a serious health hazard. This makes the mine a breeding ground for infectious diseases such as tuberculosis, and dust poisoning resulting in respiratory ailments.
Exposure to mine dust or living close to a mine is a risk factor for asthma (Vusumuzi Nkosi, 2018). People living in communities close to mine dumps show symptoms of asthma like having a wheezing chest along with a runny nose, congested nasal passages and post-nasal drip (rhino conjunctivitis). One study in South Africa reported that there was a higher prevalence of asthma symptoms such as current wheeze and rhino conjunctivitis in children and older peoples living near mine dumps (17-33 per cent). This is comparatively higher than similar studies done in the US where the rate was found to be between 4 per cent and 10 per cent and Australia (7.5 per cent to 12.5 per cent) (Vusumuzi Nkosi, 2018).
Heavy metals
Environmental pollution is one of the major challenges in modern human society (Ali and Khan, 2017). Environmental contamination and pollution by heavy metals is a threat to the environment and is of serious concern to public health (Ali et al., 2013; Hashem et al., 2017).
Since the 1940s, the rates of mobilisation and transport of heavy metals in the environment have greatly accelerated (Merian, 1984; Khan et al., 2004) due largely to rapid industrialisation and urbanisation.
Heavy metals are individual metals and metal compounds that can impact human health. These are all naturally occurring substances which are often present in the environment at low levels. In larger amounts, they can be dangerous.
Generally, humans are exposed to these metals by ingestion (drinking or eating) or inhalation (breathing). Working in or living near mining site which extracts or utilises these metals and their compounds increases ones’ risk of exposure, as does living near a site where these metals have been improperly disposed (Sabine and Wendy, 2009).
The natural sources of heavy metals in the environment include weathering of metal containing rocks and volcanic eruptions, while the principal anthropogenic sources include industrial emissions, mining, smelting, and agricultural activities like application of pesticides and phosphate fertilisers.
Combustion of fossil fuels also contributes to the release of heavy metals into the environment such as cadmium (Cd) and lead (Pb) (Spiegel, 2002). Heavy metals are persistent in the environment, contaminate the food chains, and cause different health problems due to their toxicity. Chronic exposure to heavy metals in the environment is a real threat to living organisms (Wieczorek-Da˛browska et al., 2013) including human beings.
Empirical evidence shows that metal concentrations above threshold levels affect the microbiological balance of soils and can reduce their fertility (Barbieri, 2016). In riverine ecosystems, bioaccumulation of toxic heavy metals along a food chain or food web may have adverse effects on animals and humans (Malik and Maurya, 2014).
Higher levels of heavy metals in the riverine ecosystems will have negative effects on the ecological health of the aquatic fauna and flora may contribute to declines in their populations Luo et al., 2014). Additionally, heavy metals are strong neurotoxins in fish species. The interaction of heavy metals with chemical stimuli in fish may impair the communication of fish with their surrounding environment (Baatrup, 1991).
Heavy metals have been found associated with fish deformities in both natural populations and in laboratories. Such deformities have negative effects on fish populations. Deformities affect the fish survival, growth rates, overall welfare, and external image. These deformities can serve as excellent biomarkers of environmental heavy metal pollution (Baatrup, 1991).
Hartl (2012) points that “metals, of natural or anthropogenic origin, are ubiquitous in the aquatic environment, and therefore understanding their behaviour and interaction with aquatic organisms, particularly fishes, a major source of protein for human consumption, is of a great socioeconomic importance.”

  • The author is the principal scientist at Yeyue Environmental Services