A method of calculating quartz solubilities in aqueous sodium chloride solutions

The aqueous silica species that form when quartz dissolves in water or saline solutions are hydrated. Therefore, the amount of quartz that will dissolve at a given temperature is influenced by the prevailing activity of water. Using a standard state in which there are 1,000 g of water (55.51 moles) per 1,000 cm³ of solution allows activity of water in a NaCl solution at high temperature to be closely approximated by the effective density of water, p_e, in that solution, i.e. the product of the density of the NaCl solution times the weight fraction of water in the solution, corrected for the amount of water strongly bound to aqueous silica and Na⁺ as water of hydration. Generally, the hydration of water correction is negligible.The solubility of quartz in pure water is well known over a large temperature-pressure range. An empirical formula expresses that solubility in terms of temperature and density of water and thus takes care of activity coefficient and pressure-effect terms. Solubilities of quartz in NaCl solutions can be calculated by using that equation and substituting p_e, for the density of pure water. Calculated and experimentally determined quartz solubilities in NaCl solutions show excellent agreement when the experiments were carried out in non-reactive platinum, gold, or gold plus titanium containers. Reactive metal containers generally yield dissolved silica concentrations higher than calculated, probably because of the formation of metal chlorides plus NaOH and H₂. In the absence of NaOH there appears to be no detectable silica complexing in NaCl solutions, and the variation in quartz solubility with NaCl concentration at constant temperature can be accounted for entirely by variations in the activity of water.The average hydration number per molecule of dissolved SiO₂ in liquid water and NaCl solutions decreases from about 2.4 at 200°C to about 2.1 at 350°C. This suggests that H₄SiO₄ may be the dominant aqueous silica species at 350°C, but other polymeric forms become important at lower temperatures.     

Dye removal from aqueous solutions using novel nanocomposite hydrogel derived from sodium montmorillonite nanoclay and modified starch

A novel nanocomposite hydrogels (NCHs)-based polysaccharide was synthesized by incorporating Na-montmorillonite (NaMMT) nanoparticles (NPs) into poly acrylic acid and polyacrylamide grafted onto starch [P(AA–AAm)-g-starch] hydrogel. The conditions applied in this synthesis were optimized using the Taguchi orthogonal experimental design method. The characterization of NaMMT NPs/P(AA–AAm)-g-starch NCH was performed by Fourier transform infrared, thermogravimetric analysis, scanning electron microscopy/energy-dispersive X-ray, and atomic force microscopy analyses. The resulting optimized NCH showed improved pH-dependent swelling and enhanced safranin adsorption capacity compared to pure hydrogel and NaMMT NPs. Its adsorption process could be described very well by pseudo-second-order and Elovich kinetic models. The adsorption isotherm was followed by Freundlich isotherm models. The conclusion confirms the prospect of NCH as an effective adsorbent for the adsorption of dyes from aqueous solutions.     

Amorphous silica solubilities IV. Behavior in pure water and aqueous sodium chloride,sodium sulfate,magnesium chloride,and magnesium sulfate solutions up to 350°C

Solubilities of amorphous silica were determined in separate aqueous solutions of sodium chloride, sodium sulfate, magnesium chloride, and magnesium sulfate at temperatures up to 350°C. These salts, of strong interest in hydrothermal oceanography and geothermal energy, generally ranged in concentration from zero to saturation. Solubilities in the sodium chloride solutions followed closely earlier observed decreases in sodium nitrate solutions at high temperatures.Amorphous silica solubilities were depressed most by magnesium chloride, followed by magnesium sulfate, and less by sodium chloride. As the temperature rose the relative decrease in solubility caused by added salt became smaller. Surprisingly, sodium sulfate solutions, showing little effect at 25°C, sharply raised the solubility as the temperature increased to 350°C. Plots of the logarithms of derived activity coefficients against molalities of added salt gave approximately straight lines. These plots allow simple predictions of amorphous silica solubility in single salt solutions.     

The kinetic studies of the cobalt ion removal from aqueous solutions by dolomite-based sorbent

The kinetics of Co(II) ions adsorption on thermally activated dolomite was studied with respect to the calcination temperature of natural dolomite. The sorption of Co(II) onto all samples is reasonably fast: The first 30–35 min accounts for approximately 70–80 % of Co(II) removal from feed solutions. In order to select the main rate-determining step in the overall uptake mechanism, a series of experiments were performed and data obtained were interpreted in terms of film diffusion control, intraparticle diffusion, pseudo-first-order and pseudo-second-order models. From the modeling of kinetic data, it can be concluded that adsorption of Co(II) ions from aqueous solution by heat-treated dolomite is a complex phenomenon and occurs in a mixed diffusion mode—the kinetic data are well described by the pseudo-second-order equation. The possible multistage sorption mechanism involving film diffusion and intraparticle diffusion control steps as well as chemical interaction between Co(II) ions and calcined dolomite is proposed.     

Application of agricultural fibers in pollution removal from aqueous solution

Discharging different kinds of wastewater and polluted waters such as domestic, industrial and agricultural wastewaters into environment, especially to surface water, can cause heavy pollution of this body sources. With regard to increasing effluent discharge standards to the environment, high considerations should be made when selecting proper treatment processes. Any of chemical, biological and physical treatment processes have its own advantages and disadvantages. It should be kept in mind that economical aspects are important, too. In addition, employing environment-friendly methods for treatment is emphasized much more these days. Application of some waste products that could help in this regard, in addition to reuse of these waste materials, can be an advantage. Agricultural fibers are agricultural wastes and are generated in high amounts. The majority of such materials is generated in developing countries and, since they are very cheap, they can be employed as biosorbents in water and wastewater applications. Polluted surface waters, different wastewaters and partially treated wastewater may be contaminated by heavy metals or some organic matters and these waters should be treated to reduce pollution. The results of investigations show high efficiency of agricultural fibers in heavy metal and phenol removal. In this paper, some studies conducted by the author of this article and other investigators are reviewed.     

The solubility of iron hydroxide in sodium chloride solutions

The solubility of iron(III) hydroxide as a function of pH was investigated in NaCl solutions at different temperatures (5–50°C) and ionic strengths (0–5 M). Our results at 25°C and 0.7 M in the acidic range are similar to the solubility in seawater. The results between 7.5 to 9 are constant (close to 10⁻¹¹ M) and are lower than those found in seawater (>10⁻¹⁰) in this pH range. The solubility subsequently increases as the pH increases from 9 to 12. The solubility between 6 and 7.5 has a change of slope that cannot be accounted for by changes in the speciation of Fe(III). This effect has been attributed to a solid-state transformation of Fe(OH)₃ to FeOOH. The effect of ionic strength from 0.1 to 5 M at a pH near 8 was quite small. The solubility at 5°C is considerably higher than at 25°C at neutral pH range. The effects of temperature and ionic strength on the solubility at low and high pH have been attributed to the effects on the solubility product and the formation of FeOH²⁺ and Fe(OH)₄⁻. The results have been used to determine the solubility products of Fe(OH)₃, K¹_Fe(OH)3 and hydrolysis constants, β¹₁, β¹₂, β¹₃, and β¹₄ as a function of temperature (T, K) and ionic strength (I):log K¹_Fe(OH)3 = −13.486 − 0.1856 I^0.5 + 0.3073 I + 5254/T (σ = 0.08)log β¹₁ = 2.517 − 0.8885 I^0.5 + 0.2139 I − 1320/T (σ = 0.03)log β¹₂ = 0.4511 − 0.3305 I^0.5 − 1996/T (σ = 0.1)log β¹₃ = −0.2965 − 0.7881 I^0.5 − 4086/T (σ = 0.6)log β¹₄ = 4.4466 − 0.8505 I^0.5 − 7980/T. (σ = 0.2)Both strong ethylenediaminetetraacetic acid and weak (HA) organic ligands greatly affect iron solubility. The additions of ethylenediaminetetraacetic acid and humic material were shown to increase the solubility near pH 8. The higher solubility of Fe(III) in seawater compared to 0.7 M NaCl may be caused by natural organic ligands.     

黏土质白云岩去除水中铅离子作用及机理

黏土质白云岩是新生代形成的弱固结沉积白云岩,具有丰富且开放的孔隙率及高化学反应活性,其作为环境工程材料的应用值得探讨。本文研究了黏土质白云岩去除溶液中铅的效果和作用机理,考察了黏土质白云岩除铅动力学以及初始浓度、固液比对除铅效果的影响。结果表明,黏土质白云岩与不同浓度的铅溶液反应达到平衡所需的时间不同,初始铅浓度越高反应平衡时间越长,与铅浓度100 mg/L溶液反应70 h才基本达到平衡;黏土质白云岩除铅效果主要受反应平衡后溶液的p H值控制,固液比也可影响溶液p H值;固液比越高,平衡p H值越高,铅去除越完全;黏土质白云岩去除溶液中铅离子的作用机制是其中的白云石诱导的铅沉淀,白云石溶解同时形成了碱式碳酸铅。     

Improvement of cadmium ion electrochemical removal from dilute aqueous solutions by application of multi-stage electrolysis

Improvement of cadmium ion electrochemical removal from dilute aqueous solutions in a spouted bed reactor was investigated. Enlargement of cathode surface area from 1,000 to 1,500 cm² resulted in a decrease of nearly 30 % in both of the process time and the specific energy consumption. Application of a three-stage electrolysis process for a solution containing initial concentration of 270 ppm cadmium ion, resulted in the removal of 99.9 % cadmium ion in 135 min with the specific energy consumption of 2.29 kWh/kg, 23 % less than the value of a single-stage process. For a solution with cadmium ion initial concentration of 180 ppm, 99.9 % of cadmium ion was removed in 135.5 min by application of a two-stage electrolysis process, while the specific energy consumption was 2.82 kWh/kg, 30 % less than that of a single-stage process. For a solution with cadmium ion initial concentration of 90 ppm, 99.5 % of cadmium ion was removed in 100.2 min with the specific energy consumption of 3.78 kWh/kg in a single-stage electrolysis process.     

Separation of ternary sodium chloride/Reactive Black-5 aqueous solutions using two different modules in a nanofiltration pilot plant

Nanofiltration of ternary mixtures of sodium chloride and aqueous solutions of Reactive Black-5 was studied in two different modules, namely, flat sheet and spiral wound over a wide range of operating conditions. Hydrophilized polyamide membrane with molecular weight cutoff of 150 was used for the experiments. Combined effect of dye and salt concentration, trans-membrane pressure drop, initial pH of feed solution on the permeate flux, and observed retention were investigated. Extent of color removal, chemical oxygen demand (COD), total dissolved solid (TDS), and conductivity were determined to assess performance of the membrane. The experimental results showed that both the permeate flux and observed retention decreased with increase in dye as well as salt concentration in the feed. Permeate fluxes were lower at higher pH values. Substantial removal of color was achieved in the nanofiltration experiments with a marked reduction in COD and TDS. The process allowed the production of permeate stream with great reutilization possibilities.     

Adsorption kinetics of chromium(III) removal from aqueous solutions using natural red earth

Laboratory-scale-simulated experiments were carried out using Cr(III) solutions to identify the Cr(III) retention behavior of natural red earth (NRE), a natural soil available in the northwestern coastal belt of Sri Lanka. The effects of solution pH, initial Cr(III) concentration and the contact time were examined. The NRE showed almost 100 % Cr(III) adsorption within the first 90 min. [initial [Cr(III)] = 0.0092–0.192 mM; initial pH 4.0–9.0]. At pH 2 (298 K), when particle size ranged from 125 to 180 μm the Cr(III) adsorption data were modeled according to Langmuir convention assuming site homogeneity. The pH-dependent Cr(III) adsorption data were quantified by diffused layer model assuming following reaction stoichiometries: $$ \begin{aligned} 2\, {>}{\text{AlOH}}_{{({\text{s}})}} + {\text{ Cr }}\left( {\text{OH}} \right)_{{ 2\,({\text{aq}})}}^{ + } \, \to \, \left( { {>}{\text{AlO}}} \right)_{ 2} {\text{Cr}}_{{({\text{s}})}}^{ + } + {\text{ 2H}}_{ 2} {\text{O}} \quad {\text{log K 15}}. 5 6\\ 2\, {>}{\text{FeOH}}_{{({\text{s}})}} + {\text{ Cr}}\left( {\text{OH}} \right)_{{ 2\,({\text{aq}})}}^{ + } \, \to \, \left( { {>}{\text{FeO}}} \right)_{ 2} {\text{Cr}}_{{({\text{s}})}}^{ + } + {\text{ 2H}}_{ 2} {\text{O}}\quad {\text{log K 5}}.0 8.\\ \end{aligned} $$ The present data showed that NRE can effectively be used to mitigate Cr(III) from aqueous solutions and this method is found to be simple, effective, economical and environmentally benign.     

Investigating the removal of ethylbenzene from aqueous solutions using modified graphene oxide: application of response surface methodology

This research focused on the application of response surface methodology (RSM) for the removal of ethylbenzene by the graphene oxide grafted with polymethyl vinyl ketone and aniline (GO-MVK-ANI) from wastewater. The adsorbent was prepared through polymerization of graphene oxide with methyl vinyl ketone using ammonium persulfate initiator and further modification by aniline. The synthesized material was characterized via Fourier transform infrared resonance spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and Brunauer–Emmett–Teller analysis. RSM was used to minimize the number of experiments and investigate the effect of three selected parameters (contact time, initial pH and adsorbent dose) on the removal efficiency of ethylbenzene. Additionally, the affecting parameters were optimized based on the selected target (ethylbenzene removal efficiency). The results show that 73% ethylbenzene could be adsorbed with initial ethylbenzene concentration of 20 mg/l under the optimum conditions (the contact time of 11 min, pH of 5.64 and adsorbent dose of 3.75 g/l). In this paper, high R ²-value (97.18%) for ethylbenzene removal and a good agreement with adjusted R ²-value (94.65%) indicated that the model was successful and the results demonstrated a reasonable proportion of the experimental and the predicted results.     

Adsorptive removal of pharmaceuticals and personal care products from aqueous solutions by chemically treated fly ash

This study investigated the removal efficiency of pharmaceuticals from aqueous solutions supported on chemically treated fly ash. The coal fly ash was supplied by the electric power station in Krakow, Poland. There are plenty of studies showing the utilization of fly ash as a low-cost adsorbent for wastewater containing heavy metals or dyes. Adsorption and immobilization of pharmaceuticals and personal care products on fly ash is a relatively new method but it is a very promising one. In this study, the adsorptive removal of diclofenac, ketoprofen, carbamazepine, bezafibrate, bisphenol A, 17α-ethinyl estradiol and estriol by HCl- and NaOH-treated fly ash was assessed. Chemical treatment of fly ash changed structures of particles and enhanced specific surface areas. HCl-treated fly ash was characterized by the highest BET specific surface area 47.9 m² g^?1 and unburned carbon content 8.1%. Isotherms for all compounds except for 17α-ethinyl estradiol (EE2) and estriol (E3) were linear. Higher linear regression coefficients (R ²) obtained for isotherms of EE2 and E3 show that the Freundlich model better describes their sorption. Adsorption coefficients K _d varied between 109.5 (L kg^?1) for bisphenol A and 471.5 (L kg^?1) for bezafibrate. Freundlich constants (K _F) for EE2 and E3 were 62.3 and 119.9 (µg^1?1/n L^1/n kg^?1), respectively. Acid treatment of fly ash increased adsorption of diclofenac, ketoprofen, carbamazepine, bezafibrate and bisphenol A. Comparison of the octanol–water partitioning coefficients (log K _OW) with the partitioning coefficients normalized on unburned carbon content (log K _UC) revealed similarities but no strong correlation. The increasing of unburned carbon increased sorption of compounds to fly ash.     

Adsorption of molybdenum on to anatase from dilute aqueous solutions

Adsorption of Mo on to hydrous TiO₂ (anatase) particles was investigated. Batch experiments were conducted at 19 and 90 °C over a pH range of 2 to 12 and Mo concentrations ranging from approximately 10⁻⁶ to 10⁻⁴ M. The extent of sorption was strongly dependent on pH and surface loading. Maximum sorption was observed in the acidic pH range at low surface loading. Adsorption behavior was described using the empirical Langmuir adsorption model. A constant capacitance surface complexation model was also used to fit the adsorption isotherms using a ligand exchange reaction for a hydroxyl surface site on anatase. Comparison of experimental data at two different temperatures (19 and 90 °C) indicates that Mo sorption in the acidic pH range decreases with increasing temperature.     

Hexavalent chromium removal from aqueous solutions by using low-cost biological wastes: equilibrium and kinetic studies

The batch removal of hexavalent chromium from aqueous solutions using almond shell, activated sawdust, and activated carbon, which are low-cost biological wastes under different experimental conditions, was investigated in this study. The influences of initial concentration, adsorbent dose, adsorbent particle size, agitation speed, temperature, contact time, and pH of solution were investigated. The adsorption was solution pH dependent and the maximum adsorption was observed at a solution pH of 2.0. The capacity of chromium adsorption under equilibrium conditions increased with the decrease in particle sizes. The equilibrium was achieved for chromium ion after 30?min. Experimental results showed that low-cost biosorbents are effective for the removal of pollutants from aqueous solution. The pseudo-second-order kinetic model gave a better fit of the experimental data as compared to the pseudo-first-order kinetic model. Experimental data showed a good fit with the Freundlich isotherm model. Changes in the thermodynamic parameters, including Gibbs free energy (??G_o), enthalpy (??H_o), and entropy (??S_o), indicated that the biosorption of hexavalent chromium onto almond shell, activated sawdust, and activated carbon was feasible, spontaneous, and endothermic in the temperature range 28?C50?°C.     

Adsorptive removal of azo dyes from aqueous solutions by natural bentonite under static and dynamic flow conditions

This work reports new findings on the physisorption of Foron Blue 291 on natural bentonite under both static and dynamic flow conditions of the aqueous solution that may prove important when using the adsorption technique for wastewater treatment. The quantity of dye retained by the solid matrix under both ideal exchange conditions between dyes and adsorbents given in a batch reactor and a pulse injection of dissolved azo dye in a soil column composed of a mixture of mean grain-sized sand and bentonite at different flow rates and at various mass fractions of bentonite was studied. Column experiments involving the use of a non-reactive tracer (Fluorescein) were performed to examine hydrodynamic behaviours of the clay/sand mixture studied. It is shown that advective–dispersive transport across a clay/sand mixture may be characterized by a double porosity medium. The results obtained on the reactive transport of Foron Blue 291 underscore that Foron Blue 291 adsorption depends heavily on the mass fraction of clay in a clay/sand mixture. With a clay mass fraction of 30 %, 77 % of the dissolved Foron Blue 291 mass was irreversibly removed by the adsorbent. At low flow rates, removal ratios obtained from the dynamic reactive system were similar to those obtained through previous static reactor experiments.     

共存重金属离子对针铁矿活化过硫酸盐去除水中磺胺吡啶的影响

基于硫酸根自由基的高级氧化技术能有效降解水中磺胺类药物残留。由于在自然环境中共存重金属会对环境修复效果产生一定影响,文中重点研究了不同pH环境条件下不同重金属离子对针铁矿活化过硫酸盐(PS)去除水中磺胺吡啶(SPY)的影响。不同类型重金属离子(Cu^2+、Pb^2+、Cd^2+,0.2mmol/L)在反应体系(初始条件:针铁矿,1.0g/L;PS,4mmol/L;SPY,10mg/L;pH=8.2)中对SPY的降解对比研究发现:在无重金属共存的条件下,针铁矿/PS体系降解SPY的去除率为25.2%;Pb^2+和Cd^2+对针铁矿/PS体系的影响较弱,去除率分别为30.8%和34.8%;Cu^2+的促进作用很大,可以使SPY被完全降解(100%)。机理分析认为,在针铁矿/PS体系中Pb^2+和Cd^2+主要通过影响吸附作用导致磺胺吡啶被去除,而Cu^2+主要通过自身活化PS的作用。不同pH条件(3.0,8.0,12.0)实验证实弱碱性条件下,Cu^2+/针铁矿/PS能够发挥较高的活性从而降解SPY。本文结果为采用针铁矿活化过硫酸盐技术修复类似复合污染地下水环境提供了实验依据。     

The recovery of sodium chloride from sea water

The recovery of sodium chloride from the sea has been practised since ancient times. Modern knowledge of phase rules enables us to recover fairly clean sodium chloride from sea water, which consists of a complex mixture of salts and other minerals. According to quality requirements, two procedures can be applied; solar pre-concentration of the sea water with subsequent vacuum distillation, or solar pre-concentration with subsequent over-saturation and precipitation of the salt. The individual product requirements and cost factors have to be diligently studied in order to decide which procedure is the more feasible.     

Significance of co-immobilized activated carbon and Bacillus subtilis on removal of Cr(VI) from aqueous solutions

Batch sorption system using co-immobilized (activated carbon and Bacillus subtilis) beads as adsorbent was investigated to remove Cr(VI) from aqueous solution. Fourier transform infrared spectroscopy analysis showed the functional groups of both bacteria and activated carbon in co-immobilized beads. Experiments were carried out as a function of contact time (5–300 min), initial metal concentration (50–200 mg L^?1), pH (2–8), and adsorbent dose (0.2–1 g L^?1). The maximum percentage of removal was found to be 99 %. Langmuir model showed satisfactory fit to the equilibrium adsorption data of co-immobilized beads. The kinetics of the adsorption followed pseudo-second-order rate expression, which demonstrates that chemisorption plays a significant role in the adsorption mechanism. The significant shift in the Fourier transform infrared spectroscopy peaks and a Cr peak in the scanning electron microscope–energy dispersive spectroscopy spectra further confirmed the adsorption. The results indicate that co-immobilized beads can be used as an effective adsorbent for the removal of Cr(VI) from the aqueous solution.     

Advantage of almond green hull over its resultant ash for chromium(VI) removal from aqueous solutions

The discharge of industrial effluents containing hexavalent chromium can be very harmful for the environment. Therefore, Cr(VI) should be removed from contaminated water, and especially from wastewater, to prevent its discharge into the environment. This study is aimed at analyzing the factors that affect the removal of Cr(VI) with the use of almond green hull and ash adsorbent. The effects of pH (2–10), adsorbent dose (2–24 g/L), Cr(VI) concentration (10–100 mg/L), exposure time (1–60 min), and temperature (5–50 °C) were examined. The surface morphology, pore size of adsorbent surfaces were characterized with SEM, EDX, FTIR. Maximum removal occurred at pH = 2. Results showed that the removal yield increased with the rise of exposure time and temperature. The data indicate that due to limited site on adsorbent surface, the removal efficiency decreased as initial Cr(VI) concentration increased. When the adsorbent dose was increased, the removal yield increased in the case of the bioadsorbent as well; however, in the ash adsorbent, there was an increase followed by a decreasing trend. The study highlights that almond green hull can be more efficient than its ash in the removal of Cr(VI) from aqueous solution. As a general result of study, it can be argued that almond green hull bioadsorbent and the obtained carbon are able to remove Cr(VI) from aqueous solutions; thus, they can be used as efficient and economical substitutes for existing adsorbents like activated carbon, for the removal of chromium from polluted aqueous solutions.