**2. Resources and production methods**

The resources of an element consisting of the available amount in the earth's crust, the oceans and the atmosphere, which could be identified as extractible. The part of these resources, which can be exploited in economic conditions at a given time, represents the reserves. The boundary between resources and reserves varies over time depending on the economic and technological factors of exploitation and the strategy of different states and industrial groups. The average concentrations of the main elements from the earth crust are presented in **Table 1**. As can be observed,


**Table 1.**

*The main chemical elements from the earth crust [19].*

eight elements represent almost 98.5% of the earth's crust. The base elements for geopolymerisation, i.e. oxygen (O), aluminum (Al) and silicon (Si), are situated in the first three positions and occupies almost 82% by weight from the entire earth's crust. However, because one more element (sodium (Na) and/or potassium (K) or lithium (Li)) is needed for activation, the total percentage is increased up to 88%. Moreover, considering the fact that aluminum, iron (Fe) and copper are the most extracted elements, large quantities of those goes to the mine tailing dumps, becoming a resource for geopolymers.

In order to obtain different products, the extracted resources go through a cycle of physical, chemical and mechanical processing called the circuit of materials in the production process. After extraction, the raw material undergoes a series of physical and chemical transformations until the final product is obtained (aluminum, iron, copper ingots etc.). During this transformation process, different parts from the raw material are lost, therefore, those volumes of extracted materials go to waste. Extraction, processing and manufacturing of materials require large amounts of energy and therefore production costs are highly dependent on the price of energy. From an energy point of view, organic materials are much more costeffective, because their synthesis and shaping require much lower energy consumption than metals or ceramic materials. Therefore, to reduce the production costs, the waste can be recycled and capitalized by converting it into raw materials for other products.

In the development of one technology, one material is often substituted for another, for economic or performance reasons. Thus, the car body was originally made of wood - a light material, existing in nature. Then the wood was replaced with steel sheet, a heavier but more resistant material, with controllable properties and easy to process into complex shapes. To reduce energy consumption, we switched to lighter materials. This has led to the use of thin sheets of high-strength steel, as well as very light unidirectional composite materials made of carbon fibers embedded in organic polymers.

#### **2.1 Recycled raw materials**

Anything that is not recycled or recovered from waste represents a loss of raw materials and other production factors used in the chain, in terms of production, transport and product consumption, respectively. Therefore, the environmental impacts of these secondary products are significantly higher than those associated exclusively with the effects produced during the deposition in waste dumps.

Directly or indirectly, waste affects our health and well-being in many ways: methane gas contributes to climate change, air pollutants are released into the atmosphere, drinking water sources are contaminated, crops grow on contaminated land, and fish ingest toxic chemicals, after which they reach our plates.

*The Physical and Mechanical Characteristics of Geopolymers Using Mine Tailings as Precursors DOI: http://dx.doi.org/10.5772/intechopen.97807*

### **2.2 Coal ash**

The main waste of interest to the industry, resulting from the burning of coal in thermal power plants, is the ash from thermal power plants. The interest shown by researchers in a multitude of fields is mainly due to its hydraulic properties and chemical composition (high content of oxides of silicon, aluminum, calcium and iron). Thus, it has been shown that these pozzolanic powders can become raw materials for the manufacture of technically and economically competitive materials.

Coal-ash (fly ash and bottom ash) is a result of coal burning in thermal power plants for producing energy, which is an important polluter of the environment and lands in the close areas of power plants and coal ash store units/facilities. Since the need for energy is increasing, the power plants will produce more coal-ash which is estimated approximately to 776MT per annum [20]. Because of this enormous quantity, it is necessary to make alternative technology to reduce environmental impact.

Coal ash is a silico-aluminum or low calcium material that can be used in many applications, primarily in the construction industry, e.g. concrete, pavements, recipients for containment and immobilization of radioactive wastes, refractory ceramics and because of its elemental structure, a source of geopolymerisation reaction. Due to these properties fly ash gives great mechanical strength and a good fire and chemical resistance, which influenced the researchers to find a different application of fly ash. Coal ash, especially, fly ash has been intensively studied in the geopolymers technology, therefore, this waste already presents a high interest for the researcher, and it will not be evaluated/presented intensively here [21].

### **2.3 Mine tailings**

The first stage of ore processing consists of hard rock blocks (ore) crushing and grinding up to particles with a diameter of a few centimeters or even micrometers. Secondly, the use phase is separated from the gangue part by specific means (depending on the type of ores and the used extraction technology). Mineral separation is achieved by various methods, namely: gravimetric; magnetic; electric. The surface properties of the mineral phases can also be used in the separation process. Accordingly, the products that resulted from ore processing are the concentrate and the tailings. The concentrate is processed further until the desired metal is obtained, while the tailings are deposited in different types of dumps/facilities.

A tailings dump can be defined as "the site of surface storage and the deposit of tailings extracted from the mine or tailings resulting from mechanical preparation operations". Accordingly, tailings ponds are excavated land surfaces in which liquid waste with a high content of suspensions is deposited, in order to sediment them, while mining tailings dumps are surfaces on which the material resulting from the excavation of non-metalliferous and metalliferous ores has been deposited.

As a result of the way the excavated and piled material is deposited, the piles are in the form of mounds with the appearance of a pyramid trunk, which have an upper part, more or less horizontal, which constitutes the plateau part and is bordered around the slopes.

The mineralogical and granulometric composition of the dumped material is strongly influenced by the dependence on the geological and lithological structure of the territory studied.

Under conditions of Neogene sedimentary formations composed of intercalations of fine sandy marls, sands, gravels, clays interspersed with bundles of layers of variable thickness, the uncovered and non-selectively deposited piled material
