Aluminium oxyhydroxysulfates and hydroxides are known to precipitate from mining-generated acidic, neutral and basic pH drainage waters that are enriched in potentially toxic metal(loid)s. Their role ...as medium-term (1 year) sinks of Al, As, Cu and Ni at pH values of 4, 7 and 10 was assessed using batch experiments. X-ray diffraction analysis showed that basaluminite initially formed at pH 4 and 7, whereas at pH 10, bayerite or nordstrandite (both Al(OH)3) formed. After 12 months of ageing at 20 °C, some of the pH 4 basaluminite recrystallised to form alunite, the pH 7 basaluminite recrystallised to form gibbsite, and the bayerite/nordstrandite was unchanged. At pH 4, the basaluminite took up As but did not take up Ni or Cu. By the end of the 12 months, some As was released from the basaluminite or alunite, and some Cu was taken up by these phases. At the beginning of the pH 7 experiments, As, Cu and Ni were taken up in the basaluminite, and these were retained in the gibbsite that replaced the basaluminite after 12 months. In the pH 10 experiments, only As was expelled from the bayerite/nordstrandite after 12 months. The differences in uptake of As, Cu and Ni are attributed to their aqueous speciation relative to the net surface charge of the Al oxyhydroxsulfates and hydroxides. Release of As from the pH 4 and pH 10 phases at 12 months was likely due to incorporation within the poorly crystalline original phases, followed by progressive release as the phases transformed to more crystalline minerals (at pH 4) or become more crystalline (at pH 10) with ageing. The results have significant implications for the mineralogy of Al oxyhydroxysulfates and hydroxides, and the cycling of As, Cu and Ni, in mine drainage systems.
•Role of Al oxyhydroxysulfates and hydroxides as sinks of As, Cu, Ni investigated.•Poorly crystalline phases age over 1 year to more crystalline alunite and Al(OH)3.•Arsenic uptake highest at pH 4; released to solution at pH 10 with ageing.•No Ni and Cu uptake at pH 4, complete uptake at pH 7 and 10, no change with ageing.•These Al phases can be significant hosts of As, Cu, Ni in AMD-affected environments.
The instrumentation of the root surfaces in patients with braces is complex and 100% ineffective, and it is not pleasant for the patient, which in most cases means that the patient does not attend ...with the necessary periodicity prescribed by the periodontist to perform this removal of the oral biofilm. For this reason, there are new techniques that are less invasive and more comfortable for the patient based on a decontaminating
powder with a very fine particle, 14 microns, with erythritol and chlorhexidine applied by means of an air polish that is not harmful to dental surfaces or oral mucosa.The objective is to verify in a sample of 100 patients, by means of a randomized empirical study, whether the application of erythritol powder with chlorhexidine by means of an air polisher, applied in patients with braces with periodontal disease,
can replace the instrumentation with ultrasound and gracey curettes in periodontal maintenance treatments and increase the patient’s feeling of comfort.
La instrumentación de las superficies radiculares en pacientes portadores de brackets es compleja e inefectiva al 100%, además no es agradable para el paciente, lo que en la mayoría de los casos hace que el paciente no acuda con la periodicidad necesaria pautada por el periodoncista para realizar esa eliminación del biofilm oral. Por ello, existen nuevas técnicas menos invasivas y de mayor confort para el paciente a base de un polvo descontaminante de partícula muy fina, 14 micras, con eritritol y clorhexidina aplicado mediante aeropulidor que no resulta lesiva para las superficies dentales ni la mucosa oral. El objetivo es comprobar en una muestra de 100 paciente, mediante un estudio empírico aleatorizado, si realmente la aplicación del polvo de eritritol con clorhexidina mediante aeropulidor, aplicado en los pacientes portadores de brackets con enfermedad periodontal, puede sustituir la instrumentación con ultrasonidos y curetas gracey en los tratamientos de mantenimiento periodontal y aumentar la sensación de confort del paciente.
Schwertmannite is a ubiquitous mineral formed from acid rock drainage (ARD), and plays a major role in controlling the water chemistry of many acid streams. The formation of schwertmannite was ...investigated in the acid discharge of the Monte Romero abandoned mine (Iberian Pyrite Belt, SW, Spain). Schwertmannite precipitated from supersaturated solutions mainly owing to the oxidation of Fe(II) to Fe(III) and transformed with time into goethite and jarosite. In a few hours, schwertmannite precipitation removed more than half of the arsenic load from solution, whereas the concentration of divalent trace metals (Zn, Cu, Pb, Cd, Ni, and Co) remained almost unchanged. In the laboratory, natural schwertmannite was kept in contact with its coexisting acid water in a flask with a solid–liquid mass ratio of 1:5 for 353 days. During this time, the pH of the solution dropped from 3.07 to 1.74 and the concentrations of sulfate and Fe increased. During the first 164 days, schwertmannite transformed into goethite plus H
3O-jarosite but, subsequently, goethite was the only mineral to form. Some of the trace elements, such as Al, Cu, Pb, and As were depleted in solution during the first stage as schwertmannite transformed into goethite plus H
3O-jarosite. On the contrary, the transformation of schwertmannite to goethite (with no jarosite) during the second stage released Al, Cu, and As to the solution. Despite the variation in their concentrations in solution, approximately 80% of the total Al and Cu inventories and more than 99% As and Pb remained in the solid phase throughout the entire aging process.
The Tiermas low temperature geothermal system, hosted in the Paleocene-Eocene carbonates of the Jaca-Pamplona basin, has been studied to evaluate the geochemistry and the temperature of the waters in ...the deep reservoir. These waters are of chloride-sodium type and emerge with a temperature of about 37°C. Two hydrogeochemical groups of waters have been distinguished: one with lower sulphate concentration and lower TDS (about 7500ppm) and the other with higher sulphate content and TDS values (close to 11,000ppm). There are also slight differences in the reservoir temperature estimated for each group. These temperatures have been determined by combining several geothermometrical techniques: (1) classical chemical geothermometers (SiO2-quartz, Na-K, K-Mg and Na-K-Ca), (2) specific geothermometers for carbonate systems (Ca-Mg), (3) isotopic geothermometers and, (4) geothermometrical modelling.
The good agreement in the temperature obtained by these techniques, including the cationic geothermometers which are not usually considered suitable for this type of systems, allows establishing a reliable range of temperature of 90±20°C for the low-sulphate waters and 82±15°C for the high-sulphate waters.
The mineral assemblage in equilibrium in the reservoir is assumed to be the same for both groups of waters (calcite, dolomite, quartz, anhydrite, albite, K-feldspar and other aluminosilicate phases); therefore, the differences found in the reservoir temperature and, mostly, in the geochemical characteristics of each group of waters must be due to the existence of two flow paths, with slightly different temperatures and intensity of water-rock interaction.
Anhydrite is at equilibrium in the reservoir suggesting that, although this system is hosted in carbonates, evaporites may also be present. The dissolution of halite (and the consequent increase in the chloride concentration) conditions the chemical characteristics of the waters and the equilibrium situations in the reservoir and waters acquire their chloride-sodium affinity at depth and not during their ascent to the surface.
Finally, a favourable tectonic structure for CO2 storage has been recognised in the Paleocene-Eocene carbonates of this area. Therefore, considering the characteristics of these waters (in equilibrium with calcite, dolomite and anhydrite in the reservoir), the results of this work are useful to understand some of the geochemical processes that might take place during the CO2 injection: 1) precipitation of carbonates and sulphates in the vicinity of the injection well due to desiccation of the waters and, 2) carbonate dissolution and sulphate precipitation in the long term.
•The carbonate-evaporitic geothermal system of Tiermas has been studied.•Several geothermometrical approaches have been used to obtain the reservoir T.•Although unusual, some cationic geothermometers have provided consistent results.•Halite dissolution affects the chemistry imposed by mineral equilibria at depth.•This system can be used as an analogue of a CO2 storage site.
The processes, rates, controlling factors and products of alunite (KAl3(SO4)2(OH)6) dissolution were assessed using batch dissolution experiments at pHs of c. 3, 4, 4.6, 7 and 8, and temperatures of ...c. 280, 293 and 313K. Alunite dissolution is roughly congruent at pH3, while at pH≥3.9 the process is incongruent, giving a lower Al/K ratio in solution than in the pristine alunite sample. The decrease in the Al/K ratio appears to be caused by precipitation of secondary aluminium sulfate/hydroxysulfate minerals coating the surface of the dissolving alunite, as inferred from SEM images and XPS determinations, but these minerals do not passivate the alunite surface for the time frame of the experiments (up to 400h). The lowest dissolution rates are obtained for pH4.6 and 280K. Both the temperature increase and any pH variation from that point lead to faster dissolution rates.
Based on the potassium release to solution, the influence of pH and temperature on the alunite dissolution rate for pH of 4.8 and below can be expressed as;rateK=10-4.4±0.5aH+0.10±0.02e-32±3/RT
where rateK is the alunite dissolution rate (in mol·m−2·s−1); aH+ is the activity of hydrogen ions in solution; R is the Universal gas constant (in kJ·mol−1·K−1) and T is temperature (in K).
For pH of 4.6 and above, the alunite dissolution rate can instead be expressed as;rateK=10-2.5±0.8aOH-0.14±0.02e-39±4/RT
where aOH- is the activity of hydroxyl ions in solution.
In light of the calculated values for the activation energy under the two sets of pH conditions (32±3 and 39±4kJ·mol−1), alunite dissolution appears to be surface-controlled. Examination of the most stable solvated alunite surfaces obtained by atomistic computer simulations suggests that the least energetically favourable steps during alunite dissolution are the detachment of either Al atoms or SO4 tetrahedra from exposed surfaces. Thus, these processes are most probably the rate-determining steps in alunite dissolution.
•Processes, rates, controlling factors and products of alunite dissolution were assessed using batch experiments.•Alunite dissolution was roughly congruent at pH3 and incongruent at pH≥3.9 based on Al/K dissolved ratios.•XPS, SEM and solubility calculation results point towards precipitation of secondary aluminium phases at pH>4.•Atomistic simulations suggest that detachment of Al atoms or SO4 tetrahedra are probably the rate-limiting steps.•Mathematical expressions for alunite dissolution rates (pH3 to 8 and temperatures from 279K to 313K) are proposed.
Sphalerite dissolution kinetics were studied by means of long-term (>500
h) flow-through experiments in the pH range of 1–4.2, at 25, 50 and 70
°C and at three different dissolved O
2 concentrations, ...from 0.2 to 8.7
mg
L
−1 to obtain a dissolution rate law useful to predict sphalerite long-term dissolution behavior in environments affected by acid drainage. The main factor affecting the rate of sphalerite dissolution is pH, whose increase results in a decrease in the dissolution rate, whereas rate is independent of dissolved O
2 concentration over the range of 0.2–8.7
mg
L
−1. In the range of conditions studied, the apparent activation energy was found to be 14.3
±
1.9
kJ
mol
−1. A rate law accounting for the effects of pH and temperature on the sphalerite dissolution over this range of conditions is expressed as:
R
sphalerite
=
10
-
6.49
±
0.02
e
-
14.3
±
1.9
RT
a
H
+
0.54
±
0.02
where
R
sphalerite is the sphalerite dissolution rate (mol
m
−2
s
−1),
R is the gas constant (kJ
mol
−1
K
−1),
T is the temperature (K), and
a
H
+
is the activity of H
+ ion in the solution. X-ray photoelectron spectroscopy (XPS) analyses of the reacted samples furnish evidence of the formation of a surface layer enriched in S on the sphalerite surface during dissolution. The formation of this layer does not exert any passivating effect on sphalerite long-term dissolution.
El Acto Legislativo 01 de 2005 constituyó un antes y un después en el ámbito del derecho de la seguridad social colombiano, en la medida en que se erigió como el punto de quiebre definitivo para la ...consecución de la unificación del sistema general de pensiones, lo cual se consiguió, entre otro factores, con la prohibición de las pensiones de origen convencional o arbitral.
Acid waters and sediments of the Tinto Santa Rosa acid stream (Iberian Pyritic Belt; SW, Spain) were analysed to determine the role of sedimentary phases in the behaviour of arsenic. Aqueous arsenic ...and iron concentrations decreased markedly from the adit mouth to 300
m downstream indicating iron minerals precipitation as well as arsenic sorption onto these newly-formed phases. This was confirmed by the high arsenic concentrations observed in bed-stream precipitates, which play a major role in controlling arsenic mobility. To unravel the complex nature of the AMD sediments a combination of techniques including X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), total solid digestions, X-Ray Fluorescence (XRF) and X-Ray Absorption Spectroscopy (XAS) were employed. Results showed that (1) arsenic was present predominantly in its pentavalent state; (2) upstream arsenic was sorbed onto the main phase, schwertmannite, whereas downstream it was chiefly associated with goethite and jarosite; and (3) changes in arsenic speciation with depth were observed in the consolidated terrace sediments, where arsenic appeared primarily associated with schwertmannite in the upper part of the terraces, but with goethite at depth. Arsenic mobilization was controlled by sorption onto newly formed precipitates (schwertmannite, goethite and jarosite), causing natural arsenic attenuation.
Arsenopyrite dissolution was studied by means of long-term, stirred and non-stirred flow-through experiments in the pH range of 1 to 9 at 25, 50 and 70AC and at different input dissolved-O2 ...concentrations (from 0.2 to 8.7mgLa1). At pH lower than 4, aqueous iron, which is mainly in the ferrous form, and arsenic are stoichiometrically released. Sulphur concentrations released were lower than stoichiometrically expected (S/As<1). X-ray Photoelectron Spectroscopy (XPS) and MicroRaman Spectroscopy surface analyses on reacted and unreacted samples showed an enrichment of the reacted arsenopyrite surface in sulphur and arsenic under acidic conditions. In the light of these results, the steady-state dissolution rates were estimated by the release of arsenic at pH<4 and were used to derive an empirical dissolution rate law expressed as: R arsenopyrite mol m a 2 s a 1 25 A C = 10 a 7.41 Ac 0.47 a<? a O 2 0.76 Ac 0.11 a<? a H + a 0.12 Ac 0.07 where a O2 and a H+ are the activities of hydrogen ions and dissolved oxygen, respectively and their exponents were estimated from multiple linear regression of the dissolution rates. Temperature increase from 25 to 70AC yields an apparent activation energy for the arsenopyrite oxidation by dissolved oxygen of 18.5Ac1.6kJmola1. At pH>6, aqueous iron is mainly in the ferric form and is depleted as it precipitates as Fe-oxyhydroxide onto arsenopyrite surfaces, yielding Fe/As and Fe/S less than one; between pHs 7 and 9, iron depletion is complete, and sulphur released is more abundant than arsenic released, which is precipitated as As-O phases, as confirmed by MicroRaman spectroscopy. At pHs 6-9, iron-oxyhydroxide phases and arsenic oxide phases upon the arsenopyrite surface provide an effective layer that reduces diffusion of dissolved oxygen and arsenopyrite dissolution. As coating on the arsenopyrite surface becomes the rate-limiting step, the Shrinking Core Model (SCM) allows quantification of the surface dissolution rate, especially from data obtained where the effect of coating was still negligible. The SCM also allowed us to calculate the effective coefficient for oxygen diffusion through the coating, which can vary from 10a17 to 1.5A.10a16 m2 sa1. The formation of such a coating produced a decrease in arsenic and sulphur release over time and a final surface passivation.
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