Читать книгу Application of Nanotechnology in Mining Processes - Группа авторов - Страница 13

The global human population has risen considerably since the industrial revolution and currently stands at above 7.7 billion worldwide, beyond the carrying capacity of the earth [1]. The rapid population growth is imposing tremendous challenges such as the easy spread of disease outbreaks, food scarcity, shortage of infrastructures, and insufficient communication networks, which require resources and technological advancement to ameliorate these predicaments. All resources required for this technological advancement come from mother earth and can be obtained only through two means; if they cannot be harvested (from farming), they should be mined. The mining industry plays a vital role in supplying these key resources but lacks the potential to obtain mineral resources without compromising environmental integrity [2]. Nevertheless, mining cannot be easily halted due to the growing need for mineral resources to support technological advancement required to artificially sustain the ever-increasing human population, which is beyond the earth’s carrying capacity. The mineral resources, including metals, are essential components in the advancement of several technologies, like the production of medications and vaccines, fertilizers for agricultural application to ensure food security, and the manufacture of building materials for construction of mega-infrastructures to improve road networks. They are also used as vital components to manufacture computers and cell phones for better communication networks. In addition, mining is a vital economic activity for many nations, bringing in much-needed foreign exchange earnings and employment [3]. Despite the benefits mentioned above, the legacy of mining activities includes major environmental pollution and heaps or piles of municipal solid waste (MSW) from mining [4]. For example, most valuable minerals like gold (Au), copper (Cu), sulfur (S), zinc (Zn), silver (Ag) or lead (Pb) occurs in sulfidic ore bodies (Table 1.1) with more than one type of mineralization [5]. Once these valuable metals have been extracted from their sulfidic ores, vast volumes of mine water and leftover mining solid wastes and tailings are generated, which contain most of the sulfide mineral, like pyrite. The exposure of the pyrite-containing waste to oxygen and water leads to an acid-generating material, producing acid mine drainage (AMD). The discharge of AMD is attributed to most of the contamination being transported from mining sites to the receiving environments, affecting environmental water quality [6–8] (Figure 1.1). Due to its well-known and publicized ecological impacts, many countries have adopted stringent regulations, such as Section 402 of the Clean Water Act of the Republic of South Africa, enabling mining operators to treat mine water discharging AMD [9–11].

On the one hand, treatment of AMD as required by environmental legislation has serious financial implications for the mining operators, but on the other hand, generation of AMD in former mining sites occurs long after active mining when the responsible mining companies no longer exist. Thus, treatment and remediation of AMD are an economic and financial burden to the mining company if the operation is still active, and to the community and their governments in closed or abandoned mines. Mine water discharging AMD is known to contain a consortium of dissolved elements, including precious metals and rare-earth elements (REE) [12]. Thus, AMD can be a valuable resource, especially of REE and precious metals that can generate more income and compensate for the treatment and remediation expenses of mine water and contaminated mining sites [13]. Furthermore, AMD can be regarded as an initial and natural process of hydrometallurgy of REE. However, extraction of REE from AMD is a big challenge due to the need for highly selective extraction methods, targeting only REE and leaving other metal ions dissolved in AMD to produce the required purity. Thus, recovery of REE from AMD is usually more expensive, resulting in AMD not being attractive as a source of REE. Nevertheless, using polymeric nanomaterials as hydrometallurgical extraction agents is promising to be a cost-effective and efficient method of extracting REE from AMD. One of the agent groups with high potential is Poly(amidoamine) (PAMAM) dendrimers. Consequently, this chapter discusses the application of PAMAM dendrimers as an extraction agent of REE, evaluating their performance potential and the development of methods in which they are applied.

Table 1.1 Different types of sulfide-bearing ore bodies, % content in ore body, uses, world deposit and origin [14, 15].

Sulfide ore bodies and formula	Minerals present in the ore body with % content	Application of the major elements in the ore body	Regions of major deposit of ore bodies in the world	Origin of occurrence
Arsenopyrite (FeAsS)	Arsenopyrite is the major source of arsenic, with 46% Arsenic, 34.3% Iron, and 19.7% Sulfur in the ore body. It should be noted that the arsenic content is made up of minor gold deposits.	Used in the manufacture of herbicide, alloys, wood preservative, medicine, insecticide, and rat poison.	China, Morocco, Namibia, Russia, Belgium, Iran, and Japan	Hydrothermal veins, pegmatite, contact metamorphism, and metasomatism
Bornite (Cu5FeS4)	Source of rich-grade copper metal. The ore body contains 63.3% Copper (Cu), 11.1% Iron (Fe), and 25.6% Sulfur (S)	Major applications are in electrical wires, cables, plumbing, currency, utensils, machinery, alloys, architecture, nutritional supplements, and agricultural fungicides	United States, England, Austria, Zimbabwe, Morocco, Dzhezkazgan, and Kazakhstan	In the zone of secondary supergene enrichment, source of rich copper metal
Chalcopyrite (CuFeS2)	Chalcopyrite is the principal source of copper metal and accounts for approximately 70% of the copper deposits in the world. The ore body content is made up of 34.5% Copper (Cu), 30.5% Iron (Fe), and 35.0% Sulphur (S)	Major applications of copper metal are in electrical wires, cables, plumbing, currency, utensils, machinery, alloys, architecture, nutritional supplements, agricultural fungicides, and space exploration capsules	Chile, China, Peru, United States, DRC, Australia, Russia, Zambia, Canada, and Mexico	Large, massive, irregular veins, disseminated and porphyry deposit at granitic/dioritic intrusive and SEDEX type
Cinnabar (HgS)	The ore body is a primary source of mercury. It contains 86.2% Mercury (Hg) and 13.8% Sulfur (S).	Used in the manufacturing of industrial chemicals and in electronics, thermometers, medicine, cosmetics, pigments, and fluorescent lamps. Environmentally sensitive due to health and safety regulations	China, Mexico, Kyrgyzstan, Peru, and Tajikistan	Vein-filling by recent volcanic activity and acid-alkaline hot spring
Galena (PbS)	Galena is the primary source of lead metal and one of the sources of sulfur. It contains 86.6% Lead (Pb) and 13.4% Sulfur (S).	Used as a key ingredient for paint production, used in plumbing materials, bullets, automobile batteries, alloys, sheets, radiation shields, electrodes, ceramic glazes, stained glass, and cosmetics	China, Australia, United States, Peru, Russia, Mexico, and India	Individually or associated with zinc and copper sulfide deposit
Molybdenite (MoS2)	The primary source of molybdenum with 60% Molybdenum (Mo) content and 40% Sulfur (S)	Used to coat stainless steel materials because it is resistant to corrosion, used as lubricant, tools, and high-speed steels, cast iron, electrodes, fertilizers, and for pollution control in power plants	Armenia, Canada, Chile, China, Iran, Mexico, Mongolia, Peru, Russia, and United States	High-temperature hydrothermal ore of chalcopyrite, pyrite, and molybdenite
Pentlandite (Fe, Ni)9S8	The primary source of nickel with 22% Nickel (Ni), 42% Iron (Fe), and 36% Sulfur (S)	Used in stainless steel, superalloys, electroplating, alnico magnets, coinage, rechargeable batteries, electric guitar strings, 4.6 microphone capsules, and green tinted glass	Australia, Namibia, Canada, and Brazil	The layered maficultramafic intrusion at high magmatic temperature, differential segregation
Pyrite (FeS2)	Common in all rocks and as massive sulfide deposits. It contains 46.6% Iron (Fe) and 53.4% Sulfur (S)	Mainly used to produce sulfur dioxide for paper and sulfuric acid for the chemical industry. Rarely mined for iron content due to complex metallurgy and being uneconomical commercially. Acid drainage and dust explosion are common hazards with pyrite deposits.	Italy, Spain, Kazakhstan, and United States	Common in all rocks, and as massive sulfide deposits associated with gold
Sphalerite (ZnS)	The primary source of zinc with 67% Zinc content and 33% Sulfur (S)	The main applications are in galvanizing, alloys, cosmetics, pharmaceuticals, 3.9 micronutrients for humans, animals, and plants	China, Peru, Australia, United States, Mexico, India, Bolivia, Kazakhstan, Canada, and Sweden	The majority as large SEDEX-type deposits associated with galena, chalcopyrite, and silver

Figure 1.1 Schematic showing the pathway of AMD formation, its dispersion into the environment and entrance into the food chain: The destruction of natural vegetation in search of mineral resources exposes large surface areas to weathering effects. Due to the presence of sulfide materials in these mine tailings, AMD products are formed which can be washed away into nearby streams. Aquatic life suffers the consequences due to an increase in mortality rate; meanwhile, these polluted waters can be used for irrigation and thus will bioaccumulate in plants. Once in the food chain, human lives are affected in the process.