The removal of Pb(II) from aqueous solutions by acid-modified clinoptilolite-rich tuff was investigated in this work. Clinoptilolite-rich tuff samples were treated using H2SO4 at different concentrations. Prior to and following acid treatment, the samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Fourier-transform infrared spectroscopy (FTIR). The pH of the point of zero charge (pHPZC) was also determined as part of this characterization. Batch studies were studied to investigate Pb(II) removal as a function of contact time, initial Pb(II) concentration, adsorbent dosage, and solution pH. The results of the XRD and SEM techniques showed that clinoptilolite is the main mineral of the non- and acid-treated natural zeolite samples. However, EDS analysis indicated that the Si/Al ratio increases as the exchangeable ions decrease with increasing acid concentrations. The optimum conditions for Pb(II) removal for samples with 4.37 ≤ Si/Al ≤ 7.9 were found to be as follows: Contact time of 60–360 min, pH: 6–8, and adsorbent dose of 6 mg g−1; whereas for acid-modified clinoptilolite-rich tuffs with 9.01 ≤ Si/Al ≤ 9.52, these conditions were as follows: Contact time of 1440 min, pH: 8–10, and adsorbent dose of 10 mg g−1. The experimental data were analyzed by kinetic and isotherms models. The results showed that the sorption of Pb(II) on samples with Si/Al ratios of 4.37, 5.31, and 7.91 were in agreement with the pseudo-second order and Langmuir isotherm with qm = 48.54, 37.04, and 14.99 mg g−1, respectively, while the kinetic data and isotherm for samples with 9.01 ≤ Si/Al ≤ 9.52 were found to fit the pseudo-first order and Freundlich model.
-This paper describes a shortcut procedure for batch distillation simulation with a variable reflux policy. The procedure starts from a shortcut method developed by Sundaram and Evans in 1993 and uses an iterative cycle to calculate the reflux ratio at each moment. The functional relationship between the concentrations at the bottom and the dome is evaluated using the Fenske equation and is complemented with the equations proposed by Underwood and Gilliland. The results of this procedure are consistent with those obtained using a fast method widely validated in the relevant literature.
In the present study the effect that controlled structural modifications have on the physical and conformational properties of a series of isomeric aromatic polyamides synthesized with different bulky pendant lateral groups was investigated. Physical properties of the aromatic polyamides such as thermal properties were determined by differential scanning calorimetry. Structural changes were determined by Fourier transform infrared spectroscopy, density and fractional free volume ( FFV). Light scattering and dynamic-mechanical analysis were used to characterize the thermodynamic and kinetic rigidity. Vogel's model was applied to evaluate kinetic rigidity in polyamide chains and the results were compared with physical properties data. It was found that there was a relationship between Tg and the conformational entropy determined by the structure which indicates that the higher the level of rigidity in the polyamide the higher the value of Tg. For kinetic rigidity, it was found that the relaxation time at infinite temperature Bα , was very close to the value 5 x 10-12 s, reported for other amorphous glassy materials. There was also a relationship between the activation energy of the glass transition U∞ and FFV, which is determined by the presence or absence of the bulky functional groups, indicating that the smaller the FFV, the higher the energy required for the glass transition to take place.
This document to examine the changes occurred in the flux of nutrients and NEM during dry season and rainy + north wind season in the Caleta system located within the Términos lagoon natural reserve which presents negative impacts caused by discharges of urban wastewater. Salinity, dissolved oxygen, chlorophyll a, nitrogen and phosphorus were monitored during nine months considering the dry, rainy and north wind season. Storms caused sediment disturbances which increased the amount of nutrients into the Caleta system as well as the phytoplankton production (25 mg m -3 ). The system shows longer times of water renovation during the summer (21 d) unlike (6 d) during the rainy + north wind season. On one hand, the ΔDIP values during dry season (0.0049 µmol m -2 d -1 ), establishes the system as producer and exporter of DIP into the ocean; on the other hand, the ΔDIP during rainy + north wind seasons (-0.0039 µmol m -2 d -1 ) suggests the importation of phosphorus from the ocean. Likewise, the system exports DIN (0.0031 µmol m -2 d -1 ) during the summer and imports DIN (-0.0048 µmol m -2 d -1 ), during the rainy + north wind seasons. The negative values of fixation-denitrification and NEM during the summer turn the system into a nitrogen sink. Seasonal changes were present in the system, dominated by heterotrophic NEM during summer with higher nitrogen fixation; while an autotrophic NEM dominated during winter.
The objective of this study was to assess the spatial and temporal variability of N and S atmospheric deposition and its relation with criteria air pollutants (CAPs) and meteorological conditions (MCs) in the metropolitan area of Monterrey (MAM). Atmospheric deposition was collected in 10 sampling sites during 3 climatic periods by using passive samplers based on ionic exchange resins (IERs); simultaneously, CAP and MC were monitored. Ions were extracted from IER to determine nitrate, ammonium, and sulfate levels, and deposition fluxes were estimated. On the other hand, from CAP and MC, wind and concentration roses were built to identify the exceedances of the current regulations, and relationships between CAP and meteorological conditions. It was found that only S deposition fluxes exceeded critical load values proposed in Europe, suggesting that S deposition could be a serious threat in MAM. It was found that CO in Juárez sampling site and O 3 and PM 10 in all sampling sites showed exceedances of the current regulatory limits, showing seasonal and spatial patterns similar to N and S deposition fluxes. Deposition fluxes were mapped to identify critical zones or periods in which these fluxes could be higher as a result of the prevailing meteorological conditions.
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