Life cycle assessment of mining projects for waste minimisation and long term control of rehabilitated sites (LICYMIN)

The sphere of influence of study was divided in two parts, the system and its surroundings. The region in which the mining activities take place to be considered as the system, which will be enclosed by the system boundaries. The region surrounding these boundaries is the system environment. In order to describe the mining system sufficiently and include enough detail to enable quantitative assessment of its performance during the modelling stage, the overall system was divided into the four main subsystems that are linked to each other by flows in the LCA system. These are be referred to as phases defined as follows: - Production - Processing - Waste disposal - Rehabilitation and maintenance The system was then broken up to components such that each subsystem corresponded to a small convenient size function, suitable for the technical, economic and mathematical purposes and needs and for ease of use. This small convenient function will be referred to as functional unit. The structural levels that link the mining phases indicated above with the functional units are: Phase - Process - Functional Unit. The flows of mass, energy and costs allocated to the functional unit and the relationships between inputs and outputs are identified and described as follows: Inputs: Energy, Materials (main processes, secondary processes, Services), Costs Outputs: Product, Discharges (emissions to air, effluents to surface water/groundwater, solid waste, energy, other)

An appropriate software code has to be developed to build up all possible scenarios for processing and waste management of the studied ores by relating the appropriate units for each case and calculate the inputs and outputs of the complete process scenario. The design criteria of this system are the following: - Calculating all the required variables for the alternative units applicable to the production of a metal, based on the model developed for each unit. - Taking into account the different processing and waste management scenarios for a specified metal, to select the appropriate units in order to build up a specific scenario. - To interconnect the selected units and calculate the input and output data of the complete scenario referenced to the functional units and list the functional units and their characteristics. e.g. Functional Units of Comminution Phase - For a specific flow-sheet, the system will calculate the input/output data for different capacities of the whole operation and ore particle size and chemical composition. - The information a user has to provide the system is the capacity of the whole operation, the particle size and the chemical composition of the ore. In case the user cannot provide even this information, the system uses default values, typical for each metal and type of ore. The calculated input and output data of each system along with the collected data of each are forming the data of the inventory database. This software code, combined with the inventory database, can be used as an integrated tool able to relate all the inputs and the environmentally relevant outputs (products, wastes, emissions, energy) of alternative processing and waste disposal scenarios of various metals, aiming to improve recovery, minimize waste production and ensure safe and low risk disposal with minimum impact monitoring requirements

The LICYMIN model is a tool designed to build a detailed and change-oriented Life Cycle Assessment System for mining. Three are three subsystems into which the mining system is broken down, and are covered by this model, namely Extraction (Production), Mineral Processing and Waste Remediation. The present model offers the means to the LCA practitioner to handle, manipulate, organise and analyse large amount of mining data; as well as present the results in a coherent manner. However, the conceptualisation of the LCA study and quality of the data used rest entirely on the LCA practitioner. The LCIA model interacts closely with the LCA database, which is the one responsible to store the data on the system under study; provide information for the LCA study itself, such as category indicators and factors; to provide subprograms and factors to estimate missing or poorly recorded environmental emissions during production phase, such as blasting fumes. This database was developed within the object-relational database concept model, using the software Oracle 9i Enterprise Edition. The LCA database consists of forty-four object types, forming twenty seven object tables. The display of results and/or information stored in the LCA database is carried out using the Oracle 9i Report Builder Developer tool.

All activities in the mining system are relevant to cost flows. Costs are divided into preliminary, direct, indirect, by-product credit, non-operational and environmental. Direct costs for excavation (blasting, haulage and crushing, hoisting, waste disposal, cost of closure, etc), beneficiation (crushing and screening, wet milling classification, froth flotation, dewatering, waste disposal, cost of closure etc.) have been collected and analysed. These direct costs affect the environmental costs, therefore data pertaining to the costs of environmental protection have been collected (environmental investment costs, environmental charges: fees, fines), the cost of waste disposal (hydraulic transport, distribution and silting up, clarifying, water discharge) and cost of closure, reclamation, monitoring and redevelopment (long-term costs). The sum of costs for each operational unit used in each separate process have been closely connected with the direct cost of every process defined in the LCA system. In accounting for the financial cost and benefit of alternative scenarios, economic analysis using LCC (Life Cycle Costs) for different solutions have been developed. All the cost are accounted in monetary terms, benefits are presented in quantitative and monetary (a monetary valuation study based on mainly reduction of charges and reduction of damages after environmental investment) terms.

Industrial partners used ArcView or MapInfo to integrate the already existing data and maps of the open-pit and underground mines, and other facilities around the mines into digital format. In more detail, these maps present the topography of the area (contours) and provide information on roads (main, secondary and dirt roads, trucks etc) conurbations (towns, villages), hydrology (torrents), regional geology, major tectonic features open-pit exploitations (excavation benches etc), crushing and beneficiation area infrastructure, transportation and loading points (conveyor belts, dock) on monitoring and sampling points. The information provided on mining production, mineral processing, as well as on financial provisions and energy input assisted in developing the LCIA data inventory. The information used in the inventory analysis design consisted of historical existing data integrated in digitised maps, meteorological data and those concluded by ground water, surface water and air quality measurements, employing monitoring systems. The data collected during the LICYMIN project period covers all phases of production, from the early development to end-of-life of operations and gives a profile of the extraction activities as well as a waste and emission profile. Monitoring equipment has been employed, more specifically for measurements of water quality and flow rate and dust concentration at suitably defined points.

The mining LCIA system concept proposed by Imperial College was divided into phases (mine production, processing, waste disposal and rehabilitation). The inventory system analysis work that followed on led to the decision to structure the database in specialised hierarchically organised compartments reflecting the variety and the level of detail required in each phase. The research partners carried out a detailed review of the mine production, beneficiation and mineral processing components of the LCIA system ensuring the technical completeness of each component but also achieving to express these in a structure compatible to the inventory analysis. The inventory analysis for the production and solid waste disposal phases designed by Imperial College focused on energy, manpower, material, cost and gas emission variables as primary inputs/outputs for each operational unit identified. The inventory system was developed to include the variables associated with the volume and composition of the run-of-mine, the solid waste and liquid effluents. The mineral processing inventory analysis system was developed by NTUA. The flow-sheets included in the inventory analysis system cover the phases of beneficiation and hydrometallurgical treatment and the corresponding waste disposal options of the different metallic ores. In terms of cost flows the Polish Academy of Sciences developed the corresponding inventory covering preliminary, direct, indirect, by-product credit, non-operational and environmental costs.

Resultado final

Compartir esta página

Descargar