ISSN 1105-2403
Vol. 17 (Jan-Dec 2007) Abstracts
The irresponsible management during the excavation and the mineral process of the past, as well as the arbitrary deposition of the mining wastes, the chemical reagents and other toxic materials, led to a disproportionate environmental charge of the region with toxic out-casts and toxic metals, such as Pb, As, Cd and others. The oxidation and the erosion of the sulphides at the tailing ponds and at the mineral concentrates lead to the formation of new sulphate minerals, increasing the acid drainage and the emission of the toxic metals in the hydrologic system.
The walls of the six roughly-manufactured tailing ponds have been cracked, resulting in the discharge of the metal-bearing wastes and the salt sulphates in the stream of Kirkalon and in the adjacent Eirini river. In addition, the mining area is saturated by scattered min-ing wastes and mineral concentrates, as well as by a big number of damaged barrels with various chemicals reagents, including sodium cyanide.
The first part of the work involves sampling and mineralogical-geochemical study at: 1) the tailing ponds and 2) the remains of the mineral concentrates, inside and outside of the flotation plant. The second part of this work includes the estimation of the toxic and heavy metals in the soils and the river sediments. The geochemical study is based on a total of 180 chemical analyses for major and trace elements, measured with the methods TXRF and AAS. The results focus on the basic metallic elements: Fe, Mn, Pb, Zn, Cu, As and Cd, which are present in the mined and processed ore. In this paper, 60 chemical analyses are used for the geochemical study of the tailing ponds and the mineral concentrates.
The tailing ponds contain up to 14,600 ppm Pb, up to 22,740 ppm Zn, up to 3,900 ppm Cu, up to 940 ppm As and up to 193 ppm Cd. These contents are higher in the surface of the tailing ponds basins due to the erosion and to the high concentration of the secondary salt sulphates. The surface samples contain Pb: up to 51,450 ppm, Zn: up to 57,830 ppm, Cu: up to 5,570 ppm, As: up to 1,190 ppm and Cd: up to 1,070 ppm. These results are even higher in the mineral concentrates, which are scattered within and around the plant.
The new secondary salt sulphates of halotrichite-dietrichite group and rozenite-boyleite group, which are formed by the erosion of the mining wastes and the mineral concentrates, are considered to be of big importance for the environmental charge of the area. This is caused because one of their characteristics is to absorb high concentrations of Pb, Cu and mainly S, Zn and Cd, and as they are water soluble, they play a major role in the emission of these metals in the environment and in the hydrologic system. In addition, due to the high sulphur contents, they increase the acid drainage. (Article in Greek.) © Mining & Metallurgical Annals, Hellenic Society of Mining & Metallurgical Engineers, 2007.
The sampling and the geochemical study in this second part of our work concerns: 1) the sediments of the Kirkalion stream and the river Eirini around the plant, 2) the soils around the plant area, 3) the soils of the cultivated lands around the plant and 4) the sediments along the Eirini river from the plant to the Thracean sea. In this second part of the work 120 chemical analyses of major and a number of trace elements are used, analyzed by TXRF and AAS methods. The present work deal—as in the first part—with the following heavy metals: Fe, Mn, Pb, Zn, Cu, As, and Cd which exist at the raw or processed material. In order to evaluate the impact of the various metals into the sediments and soils, especially for this work, a series of standard values have been determined, after analysing uncontami-nated sediments and soils of the studied area. These standard values are: 18 ppm for Pb, 72 ppm for Zn, 22 ppm for Cu, 15 ppm for As and 0,2 ppm for Cd.
The surface area around the plant is extremely contaminated. Most of the analyzed sam-ples contain lead and zinc more than 5,000 ppm. In places the concentrations of Pb, Zn, Cu, As and Cd reach up to 3,3400 ppm, 40,000 ppm, 2,500 ppm, 1,700 ppm and 290 ppm respectively. These values are respectively 1850, 555, 115, 110 and 1450 times higher than those of the uncontaminated sediments and soils.
At the sediments along Eirini river the highest contents of Pb is 22,830 ppm, of Zn 6,210 ppm, of Cu 760 ppm, of As 1,700 ppm and of Cd 51 ppm. These contents are respectively 1,270, 85, 35, 115 and 255 times higher than that the standard values. In the clay fraction of these samples nearly up to two to three times higher concentrations have been measured in Pb (37,800 ppm), Zn (21,550 ppm), Cu (1,030 ppm) and Cd (133 ppm), which are respectively 2100, 300, 47 and 665 times higher than the standard values. These particularly high values, into the clay fraction of the sediments, are very important because of the fact that they are transported very easily in the river waters.
The most dangerous mineral species are the various salt sulphates (their mineral chemistry have been presented in part I of this work), which are the products of weathering of the mining wastes, and which adsorb high quantities of Pb, Cu and especially of S, Zn and Cd and as they are easily dissolved in the water, they constitute the best carrier of heavy metals into the hydrologic system. (Article in Greek.) © Mining & Metallurgical Annals, Hellenic Society of Mining & Metallurgical Engineers, 2007.
On the other hand, mineral processing engineers are always interested in exceeding the strength of the materials and in producing finer particles. The numbers of particles dealing with are tremendously large and they usually measure the energy consumed in order to produce a certain size of a particulate material starting from one with larger particles.
In 1867, Rittinger assumed that the energy consumed to break a piece of rock is distributed to the surface energy of the new surfaces produced. In 1885, Kick proposed that the en-ergy required to break a piece of matter is proportional to its volume, or mass. In mineral proc-essing books the two approaches are considered as two contradicting ways to describe the energy-size relationship. However, the two approaches are independent of each other and the one does not exclude the other. Kick refers to the energy required to break the material, while Rittinger refers to how this energy is distributed in creating new surfaces. Regardless of the different approaches used, the fact is that structural engineers deal with relative large bodies in the order of meters, while mineral processing engineers deal with particles of size class in the order of micrometers. In the first case, the surface area change, due to the deformation on loading, is negligible compared to the volume of the body, while in the latter case the surface area change is considerable.
The present study examines the strength or fracture of materials and approaches the problem from the energy point of view. It proposes a model according to which the energy consumed to break a sphere of a material is partially used to deform the specimen that increases its surface area and partially is stored as internal energy in the matter. At the moment of fracture the in-ternal energy exceeds the cohesion energy of the matter and the specimen breaks. The mathematical model can explain the type of results obtained by Tavares and King for the fracture of single mineral particles.
The concept of cohesion energy, used in this work, is the same as the one used by Kick. The present model gives Kick's rule as a partial case for relatively large particles where the surface area deformation in practically negligible. The present model provides the means of measuring the surface tension of solids and their cohesion energy.
In structural mechanics the measure of the strength of a material is customarily given by the stress at the moment of breakage. However, it was shown by the present model that the stress at the moment of breakage is a function of other parameters of the material like the Young's modulus, the surface tension and the specific cohesion energy. At relatively coarse sizes the energy required for the surface deformation is negligible and the energy provided during loading is stored inside the matter as internal energy. At the moment of breakage the internal energy exhibits the cohesion energy and the specimen collapses. As a consequence, at large sizes, the specific energy of breakage and the strength of the material appear to be constant independent of the size. However, at finer sizes, the surface energy becomes important and the energy consumed by loading the specimen is not completely stored as internal energy because a considerable amount is consumed for the surface deformation. As a result the specific energy required is greater than the specific energy of cohesion and the stress, at the moment of breakage, increases. The present theory explains the apparent increase of the strength of the materials at small sizes without Griffith's assumption that the strength of materials increases at small sizes, due to less structural defects within the matter. According to the present theory Griffith's hypothesis is not necessary to explain the increase of the strength of materials at smaller sizes, but, when it happens, it simply enhances the phenomenon. (Article in Greek.) © Mining & Metallurgical Annals, Hellenic Society of Mining & Metallurgical Engineers, 2007.
This indirect presence of noise is analyzed first in the area of signal processing with the aid of the sampling theorem, according to which a band limited signal can be accurately reconstructed by its samples if the sampling frequency is grater than a critical value. The reconstruction is succeeded by the convolution of the samples sequence with the sinc funct-ion which is proved to be the covariance function of coloured noise. All other interpolation methods result by approximation of sinc with various simpler functions.
The transition to the area of geosciences is done based on the fact that if the underlying variogram function exhibits a range of influence a, then the random function representing the physical variable is approximately band limited with critical sampling size equal to a/2. (Article in Greek.) © Mining & Metallurgical Annals, Hellenic Society of Mining & Metallurgical Engineers, 2007.
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