Francisco Díaz-Fierros

EFFECTS OF IRON AND ALUMINIUM OXIDES ON THE COLLOIDAL AND SURFACE PROPERTIES OF KAOLIN

The association between clay silicates, and iron and aluminium oxides has a major influence on the chemical and physical properties of soils. In this work the interaction of a kaolin substrate with iron and aluminium oxides and/or hydroxides obtained by basification of solutions of the metal ions was compared to that of quartz. Both precipitates were obtained in the presence of the substrates.The aluminium precipitates had higher crystallinity, and thus led to smaller increases in specific surface area than those of iron, and were more effective modifiers of the surface electrical properties of the kaolin-oxide mixtures. At concentrations as low as 0.43% Al (g/100 g of substrate) the point of zero charge (PZC) of the components with variable charge was measurable, while Fe required 2.23% and gave lower PZCs than those of corresponding concentrations of Al. In both cases the PZCs shifted to higher pH as metal concentration was increased, as did the flocculation interval of colloidal suspensions of kaolin, which were close to the PZCs (where these were evaluated).The Al and Fe oxides precipitated on quartz had higher crystallinities. Both metals increased the specific surface area to a similar extent, with an almost linear relationship to metal concentration. Samples containing ca. 6.5% Fe or Al had similar or slightly higher PZCs than corresponding kaolin samples.The results were interpreted by assuming, in the case of kaolin, the union of the metal precipitate with the basal faces of the substrate, so decreasing the negative charge at this surface; and in the case of quartz, the formation of a hydroxide coating that neutralizes the negative charge on the silica surface. The difference between the results obtained for each metal was attributed to the different morphologies of their oxide precipitates.

Trace metals in river bed sediments: an assessment of their partitioning and bioavailability by using multivariate exploratory analysis.

In this study, river bed sediments were submitted to a BCR sequential extraction, together with three bioavailability tests: a weak acid elutriate (HCl), a physiologically based extraction test (PBET) and a toxicity characteristic leaching procedure (TCLP). The most remarkable features of the BCR procedure were: i) Mn and Zn showed the highest proportion of the F1 exchangeable fraction; ii) in addition to Fe, Pb and Zn were the metals with the higher percentages in the F2 reducible fraction; iii) Fe and Cu were the elements with the highest proportion of the F3 oxidizable fraction; iv) the application of Principal Component Analysis to the metals in each of the three fractions did not show clear associations between metals and sediment components considered as metal scavengers, v) considering the sum of the three BCR fractions, the elements showed a decreasing availability of: Fe > Pb > Zn > Cu > Mn > Ni > Cr. The single extractions followed a decreasing extractability order of: HCl > PBET > TCLP and they were far from the extractability deduced from the sum of fractions in the BCR extraction.

Effects of burning on nutrient balance in an area of gorse (Ulex europaeus L.) scrub

Abstract Wildfires affect nutrient balance as a result of combustion of biomass, increased surface and subsurface runoff and increased soil erosion. In the present study, nutrient inputs and outputs to burnt and unburnt Ulex scrub plots were monitored over a 2-year period. During burning, between 50 and 75% of the nutrients contained in above-ground plant tissues were directly lost due to volatilization and upward movement of particulates to the atmosphere. Only small amounts (less than 3% for all elements) were deposited at the soil surface as ash. During the first rains after burning, N, P and K losses were largely due to sediment transport in surface runoff, while Ca and Mg losses were roughly equally distributed between sediment losses and soluble-form losses (in surface runoff and subsurface flow) and Na losses were largely in soluble form. Post-burning nutrient inputs to the soil in throughfall were lower than in the control plots for N and K; in the case of the remaining elements (P, Ca, Mg and Na), inputs to the burnt plots and control plots differed little. In general, burning led to clear net losses of nutrients; annual losses were approximately 2.5–3.5 g m−2 in the case of N and approximately 6.5–9.0 g m−2 in the case of K. In the unburnt plots, by contrast, outputs were approximately equal to inputs.

Extraction study of algal pigments in river bed sediments by applying factorial designs

Phytopigment content of river bed sediments changes in response to different concentrations of available nutrients and results in a useful descriptor of their trophic state and environmental quality. In this work three incomplete factorial designs of experiments were carried out for extracting algal pigments from river sediments using dimethylsulphoxide (DMSO), methanol or acetone. The independent variables used in this study and their variation limits were: extractant:sediment ratio (1-5mL/g), temperature (40-80 degrees C) and duration of treatments (30-90min). The experimental data obtained (chlorophyll-a, chlorophyll-b and total carotenoids content) allowed the development of empirical models for each phytopigment, describing the interrelationship between operational and experimental variables by equations, including linear, interaction and quadratic terms. The experimental results obtained showed that methanol and acetone were less effective extractants for phytopigments from river sediments when compared to DMSO. The model predicted that in a single extraction using 3.6mL of DMSO/g of sediment at 38 degrees C during 40min, DMSO releases the 89% of chlorophyll-a in the range tested, whereas the best conditions for extracting chlorophyll-b and total carotenoids are achieved using 3.6-3.7mL of DMSO/g of sediment, at 64-67 degrees C for 50-51min, respectively, releasing the 76% of the chlorophyll-b and the 100% of the total carotenoids in a single extraction.

Arsenic release from river sediments in a gold-mining area (Anllóns River basin, Spain): effect of time, pH and phosphorous concentration

The release of arsenic (As) from As-rich riverbed sediments (Anllons River, Spain) was studied. In this area As is associated with pyrite and arsenopyrite and its mobilization has been favoured by past gold-mining activities. The effect of pH and phosphorous (P) concentrations, as well as the kinetics of the As release process were studied. Also, As species in solution were determined as a function of pH and time. The release of As was greatly influenced by pH and it was between 10 and 45 times higher at pH stat 10 than at pH stat 4 for all the sediments studied. The percentages of As released were between 0.1 and 0.8 % of total As at pH stat 4 but increased to values between ~7 and 11 % of total As at pH stat 10. The sediment containing the highest concentration of As released the highest amount of As (~18 mg/kg at pH stat 10). The As release kinetics was also greatly influenced by pH, mostly at alkaline pH. At pH stat 10, the amount of released As increased progressively with time. In contrast, at pH stat 4 only small differences were observed after 24 h in the amounts of As released. At alkaline pH As was released along with Fe and Al, and accompanied by organic matter dissolution. This suggests a determining role of organic matter in the As release behaviour in alkaline media. In contrast, at weakly acid pH, the release of these components was very low, suggesting that As release is controlled mainly by desorption. The speciation of As was influenced by the pH and the release time. At pH stat 4 the major species in solution were As(III) and As(V) (representing 45–69 % and 51–29 % of As released, respectively). In contrast, at pH stat 10 almost all the released As was As(V) (~99 %). The amount of As released from sediments increased with the increase in initial P concentration in solution and it experienced a dramatic increase at added P concentrations above 1 mM. Namely, the percentage of As released by 10 mM P reached ~6 % of total As for the sediments richer in As. The results obtained let us conclude that changes in pH, especially alkalinization, and inputs of P to the river markedly enhanced As mobilization from the Anllons River sediments, thus increasing health risks.

Speciation of adsorbed arsenic(V) on red mud using a sequential extraction procedure

Abstract The distribution of sorbed arsenic(V) among different geochemical fractions for arsenic(V)-loaded red mud, an oxide-rich residue from bauxite refining that has been proposed as an adsorbent for arsenic, was studied as a function of sorbed arsenic(V) concentration using a sequential extraction procedure. The release of previously sorbed arsenic(V) was also studied as a function of pH and arsenic(V) concentration. Most sorbed arsenic(V) (0.39-7.86 mmol kg-1) was associated with amorphous and crystalline Al and Fe oxides (24.1-43.8% and 24.7-59.0% of total sorbed arsenic, respectively). Exchangeable arsenic was the smallest fraction (0.4-5.2% of total sorbed arsenic). The distribution of sorbed arsenic(V) was related to the arsenic surface coverage. For arsenic surface coverages >~30% the percentage of arsenic(V) associated with the amorphous Al oxide fraction increased and that associated with the crystalline oxide fraction decreased. The arsenic(V) exchangeable fraction increased from 1.4 to 756 μmol kg-1 as surface coverage increased from 388 to 7855 μmol kg-1. The release of sorbed arsenic(V) from red mud was greater at alkaline pH values (maximum release of ~33% of previously sorbed arsenic at pH = 12), but for high arsenic(V) initial concentration (0.2 mM arsenic) considerable amounts of arsenic (6.5% of previously sorbed arsenic) were released at pH 4, in accordance with the dissolution of amorphous Al oxides in the red mud. The results obtained suggest a greater mobility of sorbed arsenic(V) as its surface concentration approaches saturation.

Study of phytopigments in river bed sediments: effects of the organic matter, nutrients and metal composition.

Phytopigment estimation has a considerable interest in the evaluation of freshwater bodies’ quality, because it takes into account the synergistic effect of nutrients like phosphorus or nitrogen on algal growth producing eutrophication. Furthermore, their increasing concentration constitutes the first step in the formation of biofilms on the surface sediments, adding a new and very important element to the dynamic nature of the surface sediments. In this study the distribution of phytoplankton—in terms of chlorophyll-a, chlorophyll-b, phaeophytin-a, phaeophytin-b, total carotenoids, total chlorophyll, and total phaeophytin—was evaluated in river bed sediments. Samples collected at sites with low levels of nutrients (P,N) and metal concentrations showed lower phytopigment concentrations than those collected at the sampling sites affected by sources of pollution. Phytoplankton concentrations were directly and highly related to the organic matter concentrations—in particular to the humic fraction—as well as to the total nitrogen (N), total phosphorus (PT) and available phosphorus (PA) concentrations in sediments. In addition, phytoplankton also correlates positively with Cu, Zn, Fe and Al extracted in oxalate, being Cu the variable that most influences the phytopigment growth. These are essential metals for the metabolism of the phytoplankton, so therefore the increase in metal concentrations can increase algal growth, unless they reach toxic levels.

Pollution potential of copper mine spoil used for road making

Abstract Copper mine spoil from Touro (A Coruna, Spain) has been used in the construction of rural roads and unasphalted tracks. Here the pollution potential of the spoil for water and soil is investigated which is derived fundamentally from the high copper content of the spoil. On the basis of a visual survey of affected roads, five sites were chosen because they seemed to be especially susceptible to pollution by runoff or sediment. Triplicate surface soil samples were taken at various distances along roads and their copper content was compared to that of triplicate pollution free control samples. Samples of sediment were taken from roadside drainage ditches at 14 locations. Six samples of water were taken from representative first order water courses receiving the runoff from the road. Extracts for determination of total Cu (Cu t ) were obtained by treating subsamples in a microwave oven with HNO 3 , HCl and HF. To estimate the copper fraction susceptible to uptake by plants (Cu e ), the samples were extracted with a NH 4 OAc/EDTA solution. The copper content of extracts was determined by atomic absorption spectrometry. Copper contents in filtered water samples were determined by inductively coupled plasma atomic emission spectroscopy. Total Cu (Cu t ) values in soils of 249.2 mg kg −1 at site 5, and 180.0 and 156.7 mg kg −1 at site 4 were the only ones which exceeded the phytotoxically excessive level of 100 mg kg −1 of Cu t . Furthermore, analysis of variance shows that it is only at sites 4 and 5 that Cu t depended significantly on sampling distance and that Cu t values differed significantly from those of the controls, making it evident that Cu pollution is derived from the spoil. Nevertheless, even at these sites, the copper fraction susceptible to uptake by plants remains low, as all mean Cu e values were −1 except the three associated with high Cu t samples, which ranged from 65.3 to 80.3 mg kg −1 . At no site did visual inspection show any signs of phytotoxicity. Total copper concentration in the −1 . In most of sediment samples, the Cu e /Cu t ratio was 8 μg l −1 , well below the threshold values established by the EC legislation on the quality of water for human consumption and for supporting fish life.

Effects of fire on cation content in water: a laboratory simulation study

Laboratory experiments were carried out to explore the effect of thermal shocks (as occur during fire) and simulated rainfall events on cation leaching dynamics in an organic rich Leptic Umbrisol soil. The soil samples were collected in the field using specially designed lysimeter boxes that allow sampling and application of thermal shock treatments and simulated rainfall while keeping the soil structure unaltered. The soil temperature during the thermal shocks and degree-hours of accumulated heat were determined, and cation (Na+, K+, Ca2+ and Mg2+) leaching was measured in surface runoff (0-cm depth) and subsurface flow (12-cm depth) samples collected from the lysimeter boxes. Important differences were found in cation leaching in relation to thermal shock: monovalent cation leaching from the soil above 200°C (68 degree-hours) and divalent cations leaching above 220°C (195 degree-hours) was higher than that seen in other treatments. In general, the amount of cations leached increased with the severity of the thermal shock; however, under moderate conditions, there was a decrease in cation leaching, mainly of monovalent ions. The exchangeable cation losses by leaching in the intense heat treatments were ~80%.

Assessment of the impact of soil heating on soil cations using the degree-hours method .

Para la evaluacion de la severidad de un incendio, tanto la duracion de la exposicion del suelo a una determinada temperatura como los factores que determinan la capacidad de transmision termica en el suelo (humedad, textura, contenido en materia organica, etc.) son parametros importantes a tener en cuenta. El presente estudio tiene como objetivo la aplicacion de la metodologia de los grados-hora (DH) en la caracterizacion de los impactos termicos de los incendios forestales en el suelo. Los tratamientos termicos se realizaron en el laboratorio usando muestras de suelo recogidas en el campo sin alterar su estructura para estudiar su efecto en el complejo de cambio del suelo. Los resultados obtenidos muestran un claro efecto en la capacidad de intercambio cationico (CIC) en funcion de los grados-hora (DH) suministrados, observandose un proceso de disminucion continuo de caracter exponencial. Esta funcion podria explicar de forma mas evidente el proceso de reduccion de la CIC que los valores maximos de temperatura alcanzados. Analizando la suma de cationes extraibles y su relacion con el tratamiento termico se observa como esta se incrementa gradualmente con la temperatura o los DH con una tendencia a la estabilizacion. Los diferentes cationes extraidos muestran un incremento progresivo con la intensidad del calentamiento, que cuando se relacionan con los DH pueden ajustarse a una funcion del tipo y=a+bxc con un elevado grado de confianza. La utilizacion de los DH como medida del calor aportado al suelo puede ser un parametro adecuado para establecer relaciones con los cambios edaficos que se pueden desencadenar en el mismo, sobre todo en el caso en el que los procesos varien de forma continua en el tiempo.