Mónica Antilén

Changes on chemical fractions of heavy metals in Chilean soils amended with sewage sludge affected by a thermal impact

Forest fires are frequent in central-southern Chile; high temperatures may affect chemical fractions of heavy metals (Cu, Zn, Ni, Pb, Cd, Mo, Cr, and Mn) naturally present in soils and those coming from sewage sludge amendment. Changes in exchangeable, sorbed, organic, carbonate, and residual heavy metals fractions, evaluated by sequential extraction, were observed after heating at 400°C in 2 amended volcanic soils. Most significant heavy metals in these samples were Cu, Zn, Pb, and Ni. A significant increment in the total content of organic matter and metal ions, such as Zn and Cu, was observed in amended soils with respect to controls. In all samples, sorbed and exchangeable forms represent <10% of the total amount, while organic and carbonate fractions represent 24 and 48%, respectively. The thermal treatment of amended soil samples results in a redistribution of the organic fraction, mainly into more insoluble carbonate and residual fractions such as oxides. Finally, the thermal impact is much more important on sewage sludge amended soils if a heavy metal remediation process is considered, reducing the mobility and solubility of heavy metals supported by sewage sludge, minimising leaching and promoting accumulations in surface horizons.

K–Ca–Mg binary cation exchange in saline soils from the north of Chile

The selectivities of the K–Ca and K–Mg cation exchange reactions were studied in batch experiments carried out with 7 Chilean saline sandy soils with low organic matter (OM) content, and rich in quartz and halite, by using the experimental Gaines and Thomas procedure and the semi-empirical Rothmund–Kornfeld approach. The soils present high reactivity to the exchange process in terms of CEC and a preference order from the surface for the cation of K > Ca > Mg. In addition, the existence of different types of exchange sites was determined; some were specific for determined cations and others presented free competition. The proposed exchange reaction for both equilibria was thermodynamically possible and the studied cations presented a decreasing mobility order K > Ca > Mg, which follows the increasing order of hydrated ionic radii. As for the Rothmund–Kornfeld semi-empirical approach, it can be employed on soils classified as Aridisol due to good fit with the experimental data. On the other hand, the Gaines and Thomas approach is only experimentally applicable since poses some restrictions concerning to salinity and carbonate contents in the studied soils.

A new methodology to evaluate adsorption capacity on nanomaterials

AbstractNanomaterials preparation has undergone great development in recent years, with important applications. The adsorbent properties of these nanomaterials cannot be always done using batch studies, because the nanometric particle size often hinders its physical separation, and this may affect the conclusions regarding adsorption studies. A new and simple method was developed, based on electrochemical measurements. For the validation process, synthetic alumina was used as adsorbent with copper solutions. The solid/solution ratio was kept constant in both the electrochemical and batch methods, optimizing in each case the adsorption equilibration time. Peak current versus Cu2+ concentration linearity was assessed from voltammograms. The electrochemical adsorption was accomplished utilizing cyclic voltammetry before and after the addition of the adsorbent. The amount of sorbed element was determined from the difference between the amount of Cu2+ added and that present in solution at equilibrium. The Langmuir, Freundlich, and Langmuir–Freundlich models were used to fit the experimental data obtained by both methods. The results of the electrochemical methodology have precision and accuracy statistically comparable to those obtained with the batch method. The electrochemical technique has the advantage of shorter adsorbent/adsorbate equilibration times than batch and do not require physical separation, allowing the adsorption on the imogolite to be established.

Mathematical modelling of temperature profile of volcanic soils affected by an external thermal impact

In this work, the soil temperature at depth was measured in the laboratory, and a mathematical model to fit the temperature profile in volcanic soils classified as Ultisols and Andisols was used. The mathematical model considered the transient heat diffusion equation, and a numerical discrete method was used to solve the equations system. The soil surface was heated for 2500 s and the temperature rose close to 700°C; the soil temperature decreased with depth; the temperature v. time curves showed a constant value when the temperature reached around 100°C, associated with water phase change and related to the water content of soils. The model was corrected by including the heat volumetric formulation. The observed relative errors are close to 10% in all fitted curves with respect to experimental data, showing the quality of the parametrisation chosen in the mathematical model. The fitting curve deviations were reduced when the actual position of thermocouples was considered, showing the sensitivity of the mathematical model. The simplified mathematical transient diffusion model proposed, which considers 2 ranges of thermal conductivity of soils and the surface temperature, was able to describe the experimental temperature profile in volcanic soils with wide differences in mineralogy, organic matter, and moisture contents.

Effect of ash from forest fires on phosphorus availability, transport, chemical forms, and content in volcanic soils

Environmental context. Intensive fertilisation and the availability of phosphorus species (less than 10%) in cultivable soils of volcanic origin are causing the accumulation of P in these soils. Phosphorus is a macronutrient that severely limits good agricultural development, so knowledge of the distribution and the different forms of P present in soils is fundamental for sustainable agricultural practice. This novel study reports the existence of increased available P in all the soils that received a load of plant ash from different tree species. Abstract. The effect associated with the distribution of ash from plantations of native, pine, and eucalyptus forests over five soils of volcanic origin was studied by means of column leaching experiments. The results show a clear increase of pH (up to 4.4 units) and of the soil’s electric conductivity (up to 21 times), whereas total extractable P content increased 3 to 10 times with respect to the control. These effects follow a sequence depending on the origin of the ash (native forest, pine, eucalyptus), concentrated in the 0.0–10.0-cm section from the top of the columns. The observed alkalinity caused an increase of available P (from 21 to 72 times with respect to the control), in addition to decreasing residual P and increasing the extraction efficiency of the method used, discarding a transformation of inorganic P into organic P. Finally, the results show that the addition of ash is a valid and complementary alternative to phosphate fertilisation.

CHARACTERIZATION OF THE POROUS STRUCTURE OF CHILEAN VOLCANIC SOILS BY NITROGEN ADSORPTION AND MERCURY POROSIMETRY

Pore volume, specific surface area (SSA), and total intragranular porosity (TIP) of Chilean soils derived from volcanic materials were studied. Soil samples involving the 0-15 and 15-30 cm depth of virgin and cultivated Collipulli (Ultisol) and Diguillin (Andisol) soils at two particle size fractions (<1 mm and <2 µm) were considered. From mercury porosimetry and N2 adsorption, mainly mesopores (pore diameter, dpore, about 10 nm) were determined for <1 mm Collipulli samples. Diguillin <1 mm soil shows macroporosity with dpore from 70 nm to 7000 nm. The clay fraction of Collipulli has macropores (dpore from 2000 nm to 40000 nm) and mesopores (dpore from 3 nm to 23 nm), while for Diguillin clay-size fraction most of the porosity comes from macropores (dpore from 50 nm to 800 nm). For all samples the SSA linearly correlates with the mesopore volume (r2=0.781; n=16) determined by N2 adsorption, and with the mesopore + macropore volume (r2= 0.771; n=12) when Collipulli <1mm samples are excluded; an inverse relationship between SSA and organic carbon content was found (r2=0.854; n=14). Thus, the SSA defined mainly by mesopores and macropores is probably related to the soil organic matter content. Mesopores and macropores mainly give the TIP, which increases as particle size decreases. No important changes in micropore and macropore volume, and in TIP were seen as result of cultivation. Mesopore volume is more important in samples dominated by kaolinite than in samples dominated by allophane (4 to 20 times). In general the soil pore distribution, its SSA and TIP are related to its mineralogy and organic matter content

Electrochemical evaluation of ciprofloxacin adsorption on soil organic matter

Over the last decade, at both a national and international level, the amount and fate of pharmaceutical residues in the environment have become of public interest. Among the several types of pharmaceutical wastes, a particular fluoroquinolone called ciprofloxacin (Cipro) is worth mentioning. On the other hand, soil organic matter (OM) has proven to be capable of generating interactions with antibiotics, which results in a decrease in their availability. Therefore, the main goal of the current work is to investigate the adsorption of Cipro on humic acids (HA), and to evaluate an electrochemical adsorption experimental design to handle the HA special particle size and solubility. S-type adsorption isotherms are observed for Cipro adsorption on HA extracted from two volcanic soils, wherein a cooperative adsorption phenomenon exists. The Langmuir–Freundlich model was utilised to obtain the best fit. This model is especially effective at fitting HA–Andisol adsorption, R2 > 0.99. Adsorption on both HA presents n > 1, strongly suggesting the existence of cooperative adsorption. This comes from the macromolecular nature of the multiple functional groups, which results in multiple interactions. The analytical results of the electrochemical methodology are statistically precise and accurate. The electrochemical technique requires shorter adsorbent–adsorbate equilibration times than traditional methods and physical separation is not needed. A detailed particle size analysis shows that the adsorption is the most significant process in OM–ciprofloxacin interaction. In relation to analytical parameters of pharmaceutical samples (ciprofloxacin), a relative standard deviation of 1.85%, a percentage error of 1.53% and a 98.5% of recovery were obtained.

Characterization of humic acids extracted from biosolid amended soils

The aim of this study was to evaluate the changes produced in the chemical, acid-base and structural properties of soil amended (biosolids) and humic acids HAs incubated at different times. In the current work the amendments were conducted with biosolids at different doses (30, 90 and 180 t ha -1 ) on

Effect of biosolids on the organic matter content and phosphorus chemical fractionation of heated volcanic Chilean soils

Biosolids produced in wastewater treatment plants with high organic matter (OM) content can be used to reclaim organic components in heated soils. The impact of biosolids amendment on soil pH, electric conductivity (EC), exchangeable cations, OM content, and phosphorus (P) chemical fractionation in 3 heated volcanic soils in southern Chile was investigated in a 4-month incubation study. In amended heated soils, pH, EC, OM content, and exchangeable cations were greater than in control soils. The control OM content was increased by biosolids, and the incubation time effect to reclaim the organic component was important in Andisols and Inceptisols. The pH decreased with incubation time, reflecting the buffer capacity of volcanic soils, and EC increased. In the heated incubated soils, inorganic P was in general higher than organic P. Phosphorus distribution showed little difference with incubation time, showing that after a short time (4 months) biosolids P was not significantly redistributed to organic P; however, more available P forms (Olsen P) were determined. It can be concluded that biosolids are a valid option for reclaiming the OM content lost in soils affected by forest fires. However, an important amount of inorganic P, strongly fixed in volcanic soils, with a relative contribution of available forms for plants, could potentially contribute to soil and water pollution.

Surfactant properties of humic acids extracted from volcanic soils and their applicability in mineral flotation processes

Surface Tension (ST) of water solutions of humic acids extracted from volcanic ash derived soils (soil humic acids, S-HA), were measured under controlled conditions of pH (13.0), temperature (25 °C) and ionic strength (NaOH 0.1M) to establish the Critical Micellar Concentration (CMC). All S-HA were characterized by elemental analysis, acid-base titration, Transmission Electronic Microscopy (TEM) micrographs, isoelectric point (IEP) and solid state 13C-NMR. After that, these humic acids were evaluated as potential biomaterials to be used in mineral flotation processes, where a series of experiments were conducted at different S-HA and molybdenite ratio (from 0.2 to 50 g ton-1) establishing the IEP of all resultant materials. The use of solid state 13C-NMR enabled the following sequence of intensity distribution areas of S-HA to be established: O/N Alkyl>Alkyl C>Aromatic C>Carboxyl. The experimental values of ST and the calculated CMC (ranging from 0.8 to 3.3 g L-1) revealed that for S-HA no relationship between the abundance groups and their behavior as surfactant materials was observed. In relation with IEP determined for all materials, the highest surface charge, which can be useful for flotation processes, was obtained with 0.2 g of S-HA per ton of molybdenite. Additionally, TEM studies confirm the formation of pseudoaggregates for all the S-HA considered. Finally, the S-HA could be considered as an alternative to chemical products and commercial humic acids materials in mineral flotation processes.