Abstract:The modelling of high pressure grinding rolls is described by the population balance model, a mass balance which includes several functions that are related to the mineral characteristics, material kinetics and operative conditions of the device. The breakage distribution function is one of these functions and refers to the way in which the daughter particles are generated by the process of comminution. The piston-die press is presented as a methodology to determine the breakage distribution function of two different materials, from the mechanical response point of view: altered granite and a cal-silicate material. The aim is to determine the relation between the operative conditions and the mineral characteristics in order to explain and predict the breakage function parameters. The materials were characterised using XRD and single compression strength tests. The altered granite is a brittle material, which generates more fines under single compression conditions compared to bed compression conditions, mainly due to the mineral composition and the response of the material to the breakage action. The cal-silicate material shows a normal trend in its breakage behaviour. As is expected, the mineralogical characterisation is a useful tool to predict the values of the parameters of the breakage distribution function.

An improved approach is presented to model the product particle size distribution resulting from grinding in high-pressure roll crusher with the aim to be used in standard high-pressure grinding rolls (HPGR). This approach uses different breakage distribution function parameter values for a single particle compression condition and a bed compression condition. Two materials were used for the experiments; altered Ta-bearing granite and a calc-silicate tungsten ore. A set of experiments was performed with constant operative conditions, while varying a selected condition to study the influence of the equipment set-up on the model. The material was comminuted using a previously determined specific pressing force, varying the feed particle size, roll speed and the static gap. A fourth group of experiments were performed varying the specific pressing force. Experimental results show the high performance of the comminution in a high-pressure environment. The static gap was the key in order to control the product particle size. A mathematical approach to predict the product particle size distribution is presented and it showed a good fit when compared to experimental data. This is the case when a narrow particle size fraction feed is used, but the fit became remarkably good with a multi-size feed distribution. However, when varying the specific pressing force in the case of the calc-silicate material, the results were not completely accurate. The hypothesis of simultaneous single particle compression and bed compression for different size ranges and with different parameters of the distribution function was probed and reinforced by various simulations that exchanged bed compression parameters over the single particle compression distribution function, and vice versa.The main advantages of HPGR lie in energy savings and the simplicity of the process [7]. However, the particle size reduction ratio is lower than that in some other types of mills, such as ball and rod mills. HPGR are used in various configurations such as pre-grinding, hybrid grinding and finish grinding, among others [4]. This is mainly due to the comminution effect under the action of high-pressure rolls, which generates many more internal fractures of particles than other devices [13][14][15], and also generates material with latent cracks for a second stage of milling or even enough to liberate the ore [4,16]. The favourable influence of HPGR performance on downstream beneficiation operations has also been proved, for example, in the ore flotation process [17]. HPGR also appears to have a less negative impact on the environment in terms of lower dust and noise emissions [18].With regard to the description of the model, the mechanism of breakage by compression and shear is dominant in roll crushers [19]. In HPGR, two main breakage mechanisms are observed: single particle compression and bed compression [20][21][22]. Single particle compression is more efficient, but larger particles cause unnecessary liner wear issues [21] and also result in the separatio...

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Four different scenarios have been studied in an underground mine, validating the results by actual data. Finding the best ventilation conditions in terms of air velocity and heat load removal. The conditions worsen as the duct is placed further from the face. While the position of the duct regarding cross-section, lower or upper side of the drift, does not give a clear conclusion about the best option, but it depends on the variable used in the analysis, either temperature, air velocity or the specific area in the working face. The findings of this study can be used to implement the most efficient auxiliary ventilation system in the mine considering the potential main issue, whether it is the working face or the place of the equipment. Besides, future scenarios can be also analysed with the model created, providing a good tool to select the auxiliary ventilation layout in each case.

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Páramo ecosystems harbor important biodiversity and provide essential environmental services such as water regulation and carbon sequestration. Unfortunately, the scarcity of information on their land uses makes it difficult to generate sustainable strategies for their conservation. The purpose of this study is to develop a methodology to easily monitor and document the conservation status, degradation rates, and land use changes in the páramo. We analyzed the performance of two nonparametric models (the CART decision tree, CDT, and multivariate adaptive regression curves, MARS) in the páramos of the Chambo sub-basin (Ecuador). We used three types of attributes: digital elevation model (DEM), land use cover (Sentinel 2), and organic carbon content (Global Soil Organic Carbon Map data, GSOC) and a categorical variable, land use. We obtained a set of selected variables which perform well with both models, and which let us monitor the land uses of the páramos. Comparing our results with the last report of the Ecuadorian Ministry of Environment (2012), we found that 9% of the páramo has been lost in the last 8 years.

The Cequia of Manresa is a 26-km open channel constructed in the fourteenth century that conveys water from the Llobregat River to the city of Manresa using an elevation difference of 10.4 m. The channel is still operational today, supplying water for domestic, industrial, and agricultural uses to an overall population of 150,000 people. A hydrometric module was constructed in 1864 to regulate the flow rate in the Cequia to under 1,000 L=s. This module was dismantled in 1959 and is currently nonoperational. This work studied the operation of the module and determined whether it met the objectives for which it was built. The module was modeled numerically. Owing to the lack of experimental measures from the module, the model was validated with an analytical model from the literature, which demonstrated its accuracy. The model was created by applying computational fluid dynamics (CFD) using FLOW-3D software. The results showed that the numerical model reproduced the dynamic behavior of the hydrometric module (transitory), and that the old automated system operated correctly, limiting the flow to the required value. The numerical models can be used as a tool for historical research.

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