An uncertainty based multi-criteria ranking system for open pit mining cut-off grade strategy selection

Cut-off grade strategy (COGS) is a concept that directly influences the financial, technical, economical, and environmental issues in relation to the exploitation of a mineral resource. Despite the simple definition of cut-off grade, the COGS problem is one of the complex and complicated problems in the mine planning process. From the optimization point of view, the COGS with an objective of maximizing the present value of future cash flows is a non-linear and a non-convex problem that even in its deterministic form can be solved using approximate optimization methods. This optimization problem will also be more complex and complicated under uncertainty conditions. This paper proposes an uncertainty based multi-criteria ranking system to investigate the problem of COGS selection considering metal price and geological uncertainties. The proposed system aims at selection of the best COGS among technically feasible alternative COGSs under uncertainty circumstances. Our developed system is based on integrating metal price and geological uncertainties as well as operating flexibility to close the mine early. We incorporate this operating flexibility into the proposed system using a Monte Carlo based real options (RO) valuation model. For this purpose, in addition to the expected value, other risk criteria are considered to rank the alternatives. These risk criteria include abilities of strategies in producing extra profits, minimizing losses, and achieving the predefined goals of the production. In this study, the technically possible COGSs are generated using the Lane comprehensive algorithm. To demonstrate the effectiveness of the proposed system, we utilize data of an Iranian gold mine. Results show that the proposed system outperforms conventional methods in the sense that it shows significantly lower average mis-ranking than the other methods and also selects a strategy with a higher value. The sensitivity analysis of the proposed system relative to the gold price shows that the system is highly dependent on the parameters of the stochastic process used to model the evolution of the metal price. Therefore, special consideration should be given in estimating stochastic process parameters.     

Influence of micropile parameters on bearing capacity of footings

Environmental Science and Pollution Research - Micropiles, on account of their versatility, can serve as both a new foundation and a long-term option for prevailing foundations without disturbing...     

Efficient microwave-assisted diastereoselective synthesis of indole-based 4,5-dihydrofurans via a one-pot,three-component reaction in water

Environmental Chemistry Letters - The combination of two or more different heterocyclic moieties in a single molecule would enhance biological activity significantly. The indole and furan scaffolds...     

Source identification of polycyclic aromatic hydrocarbons (PAHs) in sediment samples from the northern part of the Persian Gulf,Iran

Samples of surface sediments from the Iranian coast of the Persian Gulf were examined to determine the levels and sources of 15 polycyclic aromatic hydrocarbons (PAHs). Samples were collected from 30 sampling sites and analyzed for PAHs by gas chromatography–mass spectrometry (GC-MS). Total concentrations of PAHs ranged from 93 to 4,077 ng g^?1 dry weight. The PAH composition from 30 sampling sites was dominated by four-ring PAH compounds. Molecular indices based on the ratios of PAH concentrations were used to differentiate PAHs from pyrolitic to petrogenic and mixed origins. The results suggested that the main sources of PAHs in sediments from the studied region were mixed pyrolitic and petrogenic. Furthermore, benthic organisms in most of the investigated areas were not at ecotoxicological risk, according to the results from the effects range low (ERL)/effects range median (ERM) techniques suggested by the US Sediment Quality Guidelines (SQGs).     

Impact of mechanical deweeding on the phytophilous macroinvertebrate community of an eutrophic lake

The aim of the study was to estimate the impact of mechanical deweeding on the community structure of phytophilous macroinvertebrates. The eutrophic lake selected for the study was Dal Lake in the Kashmir Himalayas. The dissolved nutrient concentration was found to be highest in August and September, i.e., nitrates-nitrogen (513 μg l^?l) and total phosphorus (685 μg l^?l). During the period of investigation, a total of 22 macroinvertebrate taxa were recorded which belonged to phylum Arthropoda, Mollusca, and Annelida. The samples were collected with the help of a composite Gerking frame box and grappler. Mechanical deweeding had a profound impact on the population density of phylum Mollusca and Arthropoda followed by Annelida. However, family Tubificidae was not influenced by deweeding, as the harvester only trimmed the vegetation, and these organisms were recorded in the sediment of the lake. On average, the reference site had higher density of macroinvertebrates as compared to deweeded areas. The abundance of macroinvertebrates decreased from 200 ind. (individuals)?m^?2 in the reference site to 51 ind.?m^?2 in the deweeded site as a result of weed removal. Species richness and composition of major macroinvertebrates in harvested and unharvested areas of the lake were also dissimilar as portrayed by biotic indices vis-à-vis Shannon diversity index, evenness index, and Simpson index.     

Transforming an open dump into a sanitary landfill: a development effort in waste management

Upgrading a crude dump site into a sanitary landfill is a very challenging task; Matuail landfill site in Dhaka posed just such a challenge. From the very beginning, the existing disposal site had been used for the crude dumping of solid wastes. All types of solid wastes were haphazardly disposed of all over the site. The existing drainage channels of the dumping ground were not operational due to blockage by indiscriminate waste dumping. A large amount of leachate oozing out from the waste mixed with storm water and made the site esthetically very displeasing and environmentally unsound. This adverse situation sometimes caused disruption of the waste vehicular movement. Step-by-step improvement measures have been taken in the open dump to make it controlled and sanitary by adopting simple and locally available materials, technical guidelines, and construction techniques.     

Monitoring quantity and characteristics of municipal solid waste in Dhaka City

A reliable estimate of the quantity of solid waste generation in the city is very important for proper solid waste planning and management. However, reported estimates of solid waste generation vary widely and lead to questionability. The reported values have been derived on the assumption of demography, standard rate of waste generation by households, density values, number of trucks engaged for waste transportation and monitoring of truck movement at dump sites, etc. This diverse nature of the available data and the question of accuracy necessitate a rigorous study that has tried to document the waste quantity in the recently formulated master plan of Dhaka City. The socio-economic parameters, behavioral characteristics, generation sources, seasonality, and per capita growth rate are considered in estimating the waste quantity along with its future projections. The findings from the estimation of waste quantities state that seasonal differences in the municipal solid waste stream are not substantial. The most seasonably variable material in the municipal solid waste stream is food waste. Residential waste is relatively homogeneous. Although there are some differences in waste generation depending on demographic and other local factors, most households dispose of essentially similar types of wastes. Variation occurs in waste composition dependent upon income levels and category of sources. Variation also occurs based upon the extent of source reduction and recycling opportunities. As opportunities exist to recycle wastes, the recycling facilities might have to grow at a similar pace to the generation of waste. Physical and chemical characteristics of solid waste are important to implement the waste disposal and management plan for the selection of resource and energy recovery potentials. A number of studies have been conducted to determine the composition of wastes including moisture content and calorific value. The data show that the moisture content in city waste is significantly higher and the calorific value is much lower, which determines the viability of composting or anaerobic digestions rather than waste combustion.     

A pilot application of recycled discarded RO membranes for low strength gray water reclamation

Environmental Science and Pollution Research - Reuse of recycled RO membranes after oxidative treatment as ultrafiltration membranes promise to bring membrane filtration at par with conventional...     

Do phytotoxic allelochemicals remain in ashes after burning Chrysanthemoides monilifera subsp. monilifera (boneseed)?

Australia is facing challenges in controlling Chrysanthemoides monilifera subsp. monilifera(boneseed). However, burning has achieved some success in this regard. We aimed to investigate the comparative phytotoxicity of boneseed dried powder and ashes(burnt at 450℃ and250℃). Phenolic compounds in powder and ashes were measured using Folin–Ciocalteu assay and HPLC. The phytotoxicity of boneseed powder and ash extracts was assessed through germination bioassay on Lactuca sativa and the phytotoxicity of litter and ashes was evaluated using field soil, both in growth chamber. Burning of boneseed reduced total phenolics in ashes of boneseed organs by 99% and 100% both at high and low temperatures. The four phenolic compounds that were detected in boneseed were either absent or at negligible levels in the ashes,with inversely related to temperature. Both boneseed ash extracts and litter ash-mediated soil significantly reduced phytotoxicity displaying increased germination, biometric and biochemical parameters of test species compared with unburnt powder extracts and litter powder-mediated soil respectively, with greater reduction of phytotoxicity found for ashes produced at the lower temperature. Interestingly, the ash extracts and litter ash-mediated soil were found to stimulate some of those parameters of the test species compared to control. There was no excessive reactive oxygen species(ROS) produced in test species exposed to ash extracts compared with unburnt powder extracts. These findings suggest that burning of boneseed is an appropriate method of weed control and that this approach will reduce phytotoxicity of this species on native plants.