2.1. The Substitute Resources’ Analysis in Mining
The model of mining waste involvement in economic circulation can be built on the basis of replacing primary natural raw materials with substitute resources, which can be, for example, technogenic deposits formed as a result of mining activities. Evaluation of their use helps to determine the relative savings and the benefits of the finished products’ production from technogenic resources. In practice, the reduction in available reserves of natural raw materials and resource base depletion in mining is a general trend in the world. This circumstance is already reflected in the financial indicators of such enterprises, including growth of costs for the environment recovery. The development of the industry for the extraction and production of non-ferrous metals, including copper, is based on their involvement in economic circulation and subsoil use of the resources, which are also limited and exhaustible. In many countries, the main problem for mining enterprises’ supply of raw materials for copper production is associated with the depletion of mineral reserves, which led to the closure of mines and a reduction in copper production (
Table 1).
Table 1.
The production reduction and closure of mines for the extraction of copper ore due to the depletion of reserves in the world [
20].
Table 1.
The production reduction and closure of mines for the extraction of copper ore due to the depletion of reserves in the world [
20].
Country | Mines | Capacity, Thousand Tons | State of the Mine |
---|
USA | Miami, Freeport | 26 | Closed |
USA | Tyrone, Freeport | 43 | Reduced up to 50% |
Chile | El Abra, Freeport | 166 | Reduced up to 50% |
Chile | Collahuasi, Glen/Anglo American | 445.25 | Capacity reduction to 30 thousand tons |
USA | Ray, Asarco | 53.29 | Capacity reduction to 40% |
Congo | Katanga, Glencore | 160 | Temporary closed |
Zambia | Morani, Glencore | 110.185 | Temporary closed |
Botswana | Mowana | 10 | Closed |
In some countries, such as Chile, Australia, China, Canada, USA, and New Zealand, there is an experience on copper manufacturing from production waste [
21]. In terms of explored copper deposits, Russia accounts for 5% of world reserves and Mongolia accounts for 3%. For comparison: less than a third of technogenic waste is recycled in Russia, while in the world, this figure reaches 85–90%. Therefore, an important issue of environmental economics is the analysis and trend assessment of sustainable development of the copper industry in the context of the depletion of raw materials.
Thus, a common trend for Russia and Mongolia in copper production is the reduction of raw materials reserves against the backdrop of an increase in copper demand for national economies. Another trend is the cessation of mining enterprises due to the closure of mines. Therefore, for mining companies in Russia, Mongolia, and other countries, there is a strong search for new resources of the production by using secondary raw materials, as well as problem-solving of the accumulated environmental damage. For example, as a result of the past activities of many mining enterprises in Russia, huge numbers of the accumulated environmental damage and disturbed territories were formed. They negatively impact the environmental living conditions of the population living in such areas.
This is why the case of Erdenet Mining Corporation SOE is interesting for theory and practice, since in Mongolia, the mining sector in the medium term will remain a key factor in the country’s economic growth. Erdenet Mining Corporation SOE is one of the largest enterprises in Asia for the extraction and dressing of copper and molybdenum. It was founded in 1978 at the copper-molybdenum deposit called “Erdenetiin Ovoo”. The enterprise provides socio-economic development of the cities of Erdenet (90,000 population) and Darkhan (76,000 population). Geological exploration of the Erdenetiin Ovoo deposit began in the late 1950s. In the period from 1964 to 1968, this field was discovered. In 1976, the first explosion was carried out and an overburden had started; more than 18 million m3 of rock mass per year is mined at the Erdenetiin Ovoo deposit by the open pit method. Currently, this enterprise produces 530.0 thousand tons of copper and more than 4.0 thousand tons of molybdenum concentrate. This enterprise processes 25 million tons of ore per year, and produces 530.0 thousand tons of copper and 4.5 thousand tons of molybdenum concentrate.
The
Table 2 shows that Mongolia’s mining sector makes a significant contribution to the country’s GDP, accounting for a quarter of its income.
Table 2.
Indicators of heavy industry development in Mongolia in 2021 [
22].
Table 2.
Indicators of heavy industry development in Mongolia in 2021 [
22].
Indicator | Share |
---|
Mining sector in gross domestic product (GDP) | 24% |
Industrial sector in national economy | 69% |
Foreign direct investment | 77% |
Export | 93% |
Currently, the Erdenetiin Ovoo deposit is based on reserves of porphyry copper ores of the north-western section with a copper content of 0.54–0.57%, and a molybdenum content of 0.0165–0.0179%. At the same time, the waste rock mass contains significant residual amounts of copper, molybdenum, rhenium, silver, and other associated metals, as well as flotation reagents used in technological processes. According to experts, at this mining enterprise, the explored reserves of copper and molybdenum remain for approximately 25–30 years using the current mining technology. The negative consequences are linked to useful components decreasing in raw materials’ content, growing the costs of products. At the same time, there is a growing demand in the world, and there is a trend towards an increase in copper production.
Stabilization of world prices for raw materials, primarily for copper, to a large extent stimulated the implementation of waste processing projects and the involvement of off-balance ore in the economic turnover, which, given the low price of primary natural resources, was not profitable enough. This makes it possible to cost-effectively involve off-balance ores and the resources of technogenic deposits into economic circulation. Among the tools for reducing the environmental and economic costs of production and the processing cost, raw materials could be replaced by other, less-expensive resources.
The following case on sustainable mining could be considered. The data for the article and math calculations were the materials of Erdenet Mining Corporation SOE. To obtain finished products (copper and molybdenum) at the same level when the content of copper and molybdenum in the ore is reducing to 0.54% and 0.0167%, a further increase in ore production is necessary. At the same time, the cost of processing mined ore and producing finished products increases every year. The completed SWOT analysis showed that the strengths of Erdenet Mining Corporation SOE include the availability of substitute resources for the production and technogenic deposits as a new resource base for production. The weaknesses of the enterprise are raw material depletion, the need to implement compensatory measures due to mine’s closure, the dependence on world prices for raw materials, the lack of facilities for processing copper concentrate, and rising environmental costs. Among the threats are the closure of the enterprise’s mine in the future, instability of prices on the world market, the rising costs of employment, and environmental modernization of production. From the moment the enterprise was created and reached its design capacity, the copper content in ore indicators ranged from 0.685% to 0.833%. Later, it steadily declined from 2013 to 0.530%, and currently stands at 0.45%. Experts project it will drop to 0.21% by 2040. At the same time, in order to maintain copper concentrate production volumes, the company has started increasingly mining and processing ores with worse mineral content. Thus, when working in the combined north-western and central sections with a processing capacity of 35 million tons per year, the life of the mine can be (
Figure 1):
- (a)
with a cut-off copper content of 0.25%—36 years,
- (b)
with a cut-off copper content of 0.15%—41 years.
It is obvious that in order to maintain production volumes of finished products in conditions of a copper content decrease in the extracted raw materials, the extraction of a significantly larger volume of rock mass and ore will be required. It will be accompanied by an increase in the cost of its processing. At the same time, there is an increase in volumetric indicators associated with the extraction and processing of ore, while simultaneously reducing the ore content. At the beginning of 2018, the price of 1 ton of copper on world commodity exchanges exceeded USD 7000 (the selling price of copper concentrate from Erdenet Mining Corporation SOE was USD 1730/t). In 2017, rock production at the enterprise increased by 1810 thousand m3 relative to 2010, but ore processing remained at the same level. The production of finished products (copper) decreased significantly.
S&P Global forecast copper growth will rise to 50 million metric tons per year by 2035, exceeding total global consumption from 1990 to 2021. According to estimates by the Canadian mining corporation Ivanhoe Mines, an era of global copper shortage is coming and, in the face of growing unmet demand for this resource, prices will increase by an order of magnitude. The global trend in demand and prices for refined copper shows continuous growth against the backdrop of a significant depletion of deposits and a reduction in balance reserves of copper ores. Mineralized overburden rocks, substandard off-balance ores, and difficult-to-process oxidized and mixed ores are deposited in the mining waste rocks [
21]. Despite the difficulties of extracting copper from deposit dumps, this process is possible and economically feasible with the present technological development and taking into account the constant increase in copper prices.
The exploitation period depends on the size of the deposit and the ore content. At the same time, during the extraction process, the percentage of the ore content decreases. On average, the copper content in ores at developed deposits, for example, in Russia, is reduced to 0.5%. For example, the Gumeshevsky copper mining deposit in Russia has been in operation for 315 years; during this period, copper extraction technologies have changed many times, which has kept mining profitable.
Dumps of copper mining rocks are significant technogenic deposits, consisting of substandard, poor, and oxidized ores’ reserves [
23]. Existing leaching technologies help to use dumps as technogenic deposits and cost-effective copper extraction areas. The life of the field could be extended, as seen in
Figure 2.
The most technologically simple and least expensive methods are dump or heap leaching, which are successfully implemented in many countries. An enlarged technical and economic calculation made for the copper dump leaching of the Kalmakyr deposit has showed the economic feasibility of introducing this technology.
Figure 3 shows the dynamics of copper content in the ore of the Erdenet field. It has decreased from 0.83% to 0.35% during the period of subsoil use. The percentage of copper in the ore dumps is 0.38%, and in the oxidized dumps is 0.53%.
In 2012, the percentage of copper in the ore of the deposit and the ore of the dumps was equal. In 2021, the copper content in the ore of the deposit was at the level of copper content in the oxidized dumps. It is estimated that the average period for technogenic deposit development is 25–30 years. The main task of copper ore deposit dumps’ involvement is to rationally determine the procedure for mining based on economic, social, and environmental goals.
2.2. Algorithm of Priority and Timing Assessment for Dumps’ Use
The problem-solving requires the development of evaluation criteria each of the goals. The composition of the criteria may be different and should be determined based on the individual characteristics of the enterprise, including remoteness from populated territories occupied by dumps and tailings areas, and their impact on the environment. The following criteria were identified during a discussion with Erdenet Mining Corporation SOE and civil activists living in the mining area:
- -
Economic: profitability and volume of copper concentrate extraction;
- -
Social: the demand for the territory occupied by mining dumps and its perspectives for local development;
- -
Environmental: negative impact on the environment and possible risk of an emergency.
The specifics of the Erdenet production site require annual capital expenditures to maintain and develop. The profitability of the production is determined as a ratio of annual profit to capital costs. The economic goals’ assessment criteria are calculated as profitability in shares and the volume of concentrate recovery—in thousand tons during the period of dump development. The social and environmental goals’ criteria are assessed by experts using the Saaty scale [
23]. A set and number of criteria used for dumps evaluation does not affect the proposed process for problem-solving.
To determine a rational procedure for mining dumps of a copper ore deposit, a calculation procedure has been developed. It is performed by two stages. At the first stage, it is necessary to determine the priority of using dumps, based on all applicable criteria. During such an assessment, all criteria must be used simultaneously with their weight. Among well-known ranking methods, the analytic hierarchy process (AHP) satisfies the formulated conditions. To apply this method, you should use the Saaty scale, which is already included in the expert assessment of socio-ecological criteria [
24,
25].
Therefore, it is necessary to convert the evaluation criteria into this scale [
26,
27,
28,
29,
30,
31,
32,
33,
34,
35,
36], to quantify an economic goal using an incremental step based on formula:
where
—criterion value for the
i-th dump
.
Using the found step , an individual scale ranging from the minimum to maximum value for the used criterion can be obtained. It corresponds to the Saaty scale. For example, if the maximum value of production profitability among the analyzed dumps is 4.22, and the minimum is 1.36, then the step value is . Based on this step, a gradation of production profitability has been obtained. It is associated with lexical units and the Saaty scale.
The algorithm for the priority determining of compared objects based on the hierarchy analysis method is known and widely used in practical calculations [
30,
31,
32,
33,
34,
35]. It is not advisable to dwell on it. The use of the hierarchy analysis method makes it possible to obtain priority
for the dumps’ development
.
The second stage of problem-solving is to determine the rational sequence of dump mining [
22]. It will ensure the first-priority selection of the highest priority dumps based on the annual volume of allocated financial resources
in year
t to ensure annual capital costs
for mining maintenance and development during dumps’ processing
. The sequence of dump mining is identified by the required start
and end
dates for dump mining with a duration of
. The heuristic algorithm is developed and used for the rational sequence of dumps’ mining determination:
Step 1. Specifying a set of analyzed dumps for which rational sequence and timing of mining has to be found.
Step 2. Setting the current time and values for the volume of financing of capital investments ,
Step 3. Selection of the dump
with the highest priority within the available financial resources to ensure capital costs for the mining maintenance and development:
ind—operation of selecting the index (dump number) at which the maximum value is achieved if financing is possible at the current time , i.e., .
Step 4. Check: if such a dump is not selected, then move on to the next year ; go to step 3. Otherwise, go to step 5.
Step 5. Calculation of time for dump development
:
Step 6. Adjustment of remaining funding amounts after choosing a dump
:
Step 7. Elimination from the set of unselected dumps
Step 8. Check whether all dumps are included in the mining sequence, i.e., ? If yes, then the calculations are complete; otherwise, go to step 3. The proposed algorithm can be easily implemented as a VBA-Excel macro.