Removal of Cadmium from Dilute Solutions by Hydroxyapatite. II. Flotation Studies

Sawdust for the Removal of Heavy Metals from Water: A Review

The threat of the accumulation of heavy metals in wastewater is increasing, due to their abilities to inflict damage to human health, especially in the past decade. The world’s environmental agencies are trying to issue several regulations that allow the management and control of random disposals of heavy metals. Scientific studies have heavily focused on finding suitable materials and techniques for the purification of wastewaters, but most solutions have been rejected due to cost-related issues. Several potential materials for this objective have been found and have been compared to determine the most suitable material for the purification process. Sawdust, among all the materials investigated, shows high potential and very promising results. Sawdust has been shown to have a good structure suitable for water purification processes. Parameters affecting the adsorption mechanism of heavy metals into sawdust have been studied and it has been shown that pH, contact time and several other parameters could play a major role in improving the adsorption process. The adsorption was found to follow the Langmuir or Freundlich isotherm and a pseudo second-order kinetic model, meaning that the type of adsorption was a chemisorption. Sawdust has major advantages to be considered and is one of the most promising materials to solve the wastewater problem.

Evaluation of Groundwater and Grey Water Contamination with Heavy Metals and Their Adsorptive Remediation Using Renewable Carbon from a Mixed-Waste Source

The contamination of water sources with heavy metals is a serious challenge that humanity is facing worldwide. The aim of this work was to evaluate and remediate the metal pollution in groundwater and greywater resources from Riyadh, Saudi Arabia. In addition, we investigated the application of ultrasonic power before adsorption to assess the dispersion of renewable carbon from mixed-waste sources (RC-MWS) as an adsorbent and enhance the water purification process. The renewable carbon adsorbent showed high ability to adsorb Pb(II), Zn(II), Cu(II), and Fe(II) from samples of the actual water under study. The conditions for the remediation of water polluted with heavy metals by adsorptive-separation were investigated, including the pH of the adsorption solution, the concentration of the heavy metal(s) under study, and the competition at the adsorption sites. The enhanced adsorption process exhibited the best performance at a pH of 6 and room temperature, and with a contact time of 60 min. Kinetic studies showed that the pseudo-second-order kinetic model was fitted with the adsorption of Pb(II), Zn(II), Cu(II), and Fe(II) onto the RC-MWS. The adsorption data were well fitted by Langmuir isotherms. The Freundlich isotherm was slightly fitted in the cases of Cu(II), Zn(II), and Fe(II), but not in the cases of Pb(II). The developed adsorption process was successfully applied to actual water samples, including water samples from Deria and Mozahemia and samples from clothes and car washing centers in Riyadh city.

Comparison of Jordanian and standard diatomaceous earth as an adsorbent for removal of Sm(III) and Nd(III) from aqueous solution

In this study, Jordanian diatomaceous earth (JDA) and commercial diatomaceous earth (standard diatomaceous earth, SDA) were used for adsorption of samarium (Sm)(III) and neodymium (Nd)(III) ions from aqueous solutions using batch technique as a function of initial concentration of metal ions, adsorbent dosage, ionic strength, initial pH solution, contact time, and temperature. Both adsorbents were characterized by Fourier transform infrared (FTIR), X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller surface area, and cation exchange capacity (CEC). Maximum metal ion uptake was observed after 100 min of agitation, and the uptake has decreased with increasing temperature and reached a maximum at pH ≈ 5. Different types of adsorption isotherms and kinetic models were used to describe the Nd(III) and Sm(III) ion adsorption. The experimental data fitted within the following isotherms in the order Langmuir > Dubinin-Radushkevich (DR) > Freundlich and the pseudo-second-order kinetic model based on their coefficient of determination (R²), chi-square (χ²), and error function (F_error%) values. Maximum adsorption uptakes, according to the Langmuir model, were obtained as 188.679 mg/g and 185.185 mg/g for Sm(III) and 169.492 mg/g and 149.254 mg/g for Nd(III) by JDA and SDA, respectively. The results of thermodynamic parameters showed that the adsorption of Sm(III) and Nd(III) ions onto JDA and SDA is a feasible, spontaneous, exothermic, and entropy driven. The best recovery for Sm(III) and Nd(III) was obtained when the 0.05 M EDTA + 0.05 M H₃PO₄ mixture was used as an eluent.

Biosorption of copper, zinc, cadmium and chromium ions from aqueous solution by natural foxtail millet shell

The industrial effluents discharge including heavy metals drain into the river, which has given rise to many problems of hazarding aquatic ecosystems and human health. Biosorption serves as the adsorption of heavy metals onto a natural adsorbent, it is becoming a potential alternative for toxic metals removal from industrial effluents in the last decades. The objectives of present research were to investigate the biosorption behaviors and the mechanisms of copper (Cu), zinc (Zn), cadmium (Cd) and chromium (Cr) ions, respectively onto foxtail millet shell as a new natural biosorbent in aqueous solution. The effects of pH (2.0-6.0), contact time (5.0-240.0 min), initial metal ions concentration (25.0-300.0 mg/L), particle size (0.25-2.0 mm) and biosorbent dosage (1.0-6.0 g/L) on the adsorption efficiency of the target metals using foxtail millet shell were evaluated in batch experiments. The models of isotherms and kinetics were used to assess the removal behaviors of Cu, Zn, Cd and Cr ions from aqueous solution by foxtail millet shell. The results showed that the best fitting equilibrium isotherm models for Cu, Zn, Cd and Cr ions were Freundlich (Cu and Zn) and Langmuir (Cd and Cr), respectively under the proper adsorption conditions. The maximum biosorption capacities were 11.89, 10.59, 12.48 and 11.70 mg g^-1 of Cu, Zn, Cd and Cr, respectively by terms of Langmuir model. The kinetics of biosoption the target metal ions processes were best explained by pseudo-second-order kinetic model. Furthermore, pseudo-second-order and intraparticle diffusion models were cooperative mechanism during the whole biosorption. In addition, the pores on the surface of the shell were covered and then became smooth after biosorption through Scanning electron microscope (SEM) revealed, which demonstrated that the target metal ions were adsorbed by foxtail millet shell. The results of Energy dispersive spectrometer (EDS) further gave evidences that Cu, Zn, Cd and Cr ions were adsorbed onto surface of the adsorbent, respectively. Analysis of Fourier transform infrared spectroscopy (FTIR) demonstrated that various functional groups, such as C-H, C˭O, C˭C, C-O, O-S-O and Si-O groups were engaged in the interaction between foxtail millet shell and Cu, Zn, Cd and Cr ions. This paper provided evidences that foxtail millet shell was a potential and efficient biosorbent on removal of Cu, Zn, Cd and Cr ions from aqueous solutions, due to its high biosorption availability, capacity and low cost.

Carbonized medlar-core particles as a new biosorbent for removal of Cu(2+) from aqueous solution and study of its surface morphology

The objective of this study was to investigate the use of carbonized medlar-core particles as a new biosorbent to remove Cu(2+) from aqueous solution. Fourier transform infrared spectroscopy and scanning electron microscopy were used to characterize the biosorbent. This paper reports the effects of adsorbent dose, pH, temperature and concentration of adsorbate. Batch isotherm studies were also performed to understand the ability of the adsorbent. The adsorption behavior of the Cu(2+) was studied using Langmuir and Freundlich adsorption isotherm models. The maximum adsorption capacity determined from the Langmuir adsorption equation has been found as 43.478 mg.g(-1) at 298.15 K. The adsorption of Cu(2+) by medlar core in carbonized form was spontaneous and endothermic. It was also found that the biosorption of Cu(2+) followed second-order kinetics. Carbonized medlar-core particles showed great potential in aqueous solution due to the high adsorption capacity.

Batch Sorption Experiments: Langmuir and Freundlich Isotherm Studies for the Adsorption of Textile Metal Ions onto Teff Straw (Eragrostis tef) Agricultural Waste

Adsorption of heavy metals (Cr, Cd, Pb, Ni, and Cu) onto Activated Teff Straw (ATS) has been studied using batch-adsorption techniques. This study was carried out to examine the adsorption capacity of the low-cost adsorbent ATS for the removal of heavy metals from textile effluents. The influence of contact time, pH, Temperature, and adsorbent dose on the adsorption process was also studied. Results revealed that adsorption rate initially increased rapidly, and the optimal removal efficiency was reached within about 1 hour. Further increase in contact time did not show significant change in equilibrium concentration; that is, the adsorption phase reached equilibrium. The adsorption isotherms could be fitted well by the Langmuir model. The value in the present investigation was less than one, indicating that the adsorption of the metal ion onto ATS is favorable. After treatment with ATS the levels of heavy metals were observed to decrease by 88% (Ni), 82.9% (Cd), 81.5% (Cu), 74.5% (Cr), and 68.9% (Pb). Results indicate that the freely abundant, locally available, low-cost adsorbent, Teff straw can be treated as economically viable for the removal of metal ions from textile effluents.

Kinetic and thermodynamics of the removal of Zn2+ and Cu2+ from aqueous solution by sulphate and phosphate-modified Bentonite clay

The modification of pristine Bentonite clay with sulphate and phosphate anions was found to increase its cation-exchange capacity (CEC), adsorption capacity and overall pseudo-second order kinetic rate constant for the adsorption of Cu(2+) and Zn(2+). Modification with sulphate and phosphate anion decreased the specific surface area of pristine Bentonite clay. Phosphate-modified Bentonite clay was found to give the highest adsorption capacity for both metal ions. The adsorption process was observed to be endothermic and spontaneous in nature for both metal ions with Zn(2+) being more adsorbed. Modification with phosphate anion increased the spontaneity of the adsorption process. The effective modification of pristine Bentonite clay with sulphate anion was confirmed from hypochromic shifts in the range of 13-18 cm(-1) which is typical of physisorption while modification with phosphate anion was confirmed by its hyperchromic shifts typical of chemisorption in the infrared red region using Fourier transformed infrared spectroscopy (FTIR). Using the model efficiency indicator, kinetic data were found to show very strong fit to the pseudo-second order kinetic model implying that the adsorption of Cu(2+) and Zn(2+) were basically by chemisorption.

Equilibrium and kinetics of biosorption of cadmium(II) and copper(II) ions by wheat straw

Biosorption equilibrium and kinetics of Cd(2+) and Cu(2+) ions on wheat straw, Triticum aestivum, in an aqueous system were investigated. Among the models tested, namely the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherms, the biosorption equilibrium for both Cd(2+) and Cu(2+) was best described by the Langmuir model. The Langmuir biosorption capacity for Cd(2+) was about 27% higher than that for Cu(2+). It was also found that biosorption of Cd(2+) and Cu(2+) by wheat straw followed second-order kinetics. The equilibrium amount of metal ions adsorbed onto the wheat straw increased with increasing of pH from 4.0 to 7.0, and the effect was more pronounced for Cd(2+) than for Cu(2+). The equilibrium adsorbed amount also increased with the initial concentration of the metal ions, as expected. On the other hand, an increase of temperature from 25 to 30 degrees C only enhanced the biosorption of Cd(2+) and Cu(2+) slightly. The apparent temperature independence and the strong pH dependence of the amount of metal ions adsorbed along with moderate mean free energies of biosorption (between 8.0 and 12.9 kJ mol(-1)) altogether indicate that biosorption of Cd(2+) and Cu(2+) by wheat straw might follow a chemisorption mechanism.

Adsorptive separation of cadmium from aqueous solutions and wastewaters by riverbed sand

Application of riverbed sand for the adsorptive separation of cadmium(II) from aqueous solutions has been investigated. Removal increased from 26.8 to 56.4% by decreasing the initial concentration of cadmium from 7.5 x 10(-5) to 1.0 x 10(-5)M at pH 6.5, 25 degrees C temperature, agitation speed of 100 rpm, 100 microm particle size and 1.0 x 10(-2) NaClO4 ionic strength. Process of separation is governed by first order rate kinetics. The value of rate constant of adsorption, k(ad), was found to be 2.30 x 10(-2)per min at 25 degrees C. Values of coefficient of mass transfer, beta L, were calculated and its value at 25 degrees C was found to be 1.92 x 10(-2)cm/s. Values of Langmuir constant were calculated. Values of thermodynamic parameters delta G0, delta H0 and delta S0 were also calculated and were recorded as -0.81 kcal/mol, -9.31 kcal/mol and -28.10 cal/mol at 25 degrees C. pH has been found to affect the removal of cadmium significantly and maximum removal, 58.4%, has been found at pH 8.5. Process can be used for treatment of cadmium(II) rich wastewaters.

Adsorption of Cu(II), Ni(II) and Zn(II) on modified jute fibres

The potential of a lignocellulosic fibre, jute, was assessed for adsorption of heavy metal ions like Cu(II), Ni(II) and Zn(II) from their aqueous solutions. The fibre was also used as adsorbent after chemically modifying it by two different techniques viz, loading of a dye with specific structure, C.I. Reactive Orange 13, and oxidising with hydrogen peroxide. Both the modified jute fibres gave higher metal ion adsorption. Thus, the dye loaded jute fibres showed metal ion uptake values of 8.4, 5.26 and 5.95 mg/g for Cu(II), Ni(II) and Zn(II), respectively, while the corresponding values for oxidised jute fibres were 7.73, 5.57 and 8.02 mg/g, as against 4.23, 3.37 and 3.55 mg/g for unmodified jute fibres. Adsorption isotherm models indicated best fit for Langmuir model for the modified jute fibres. The adsorption values decreased with lowering of pH. The desorption efficiency, regenerative and reuse capacity of these adsorbents were also assessed for three successive adsorption-desorption cycles. The adsorptive capacity was retained only when the caustic soda regeneration is carried out as an intermediate step after desorption. Possible mechanism has been given.

Flotation of metal-loaded clay anion exchangers. Part I: the case of chromates

Synthetic hydrotalcite-like layered materials are known for their ability to remove anions, like the chromates. These sorbents usually exist in powder form, thereby exhibiting high surface area and rapid kinetics for adsorption, but presenting appreciable problems in the subsequent solid/liquid separation process. Almost complete removals were obtained in this paper, from batchwork dispersed-air flotation in presence of a flocculant. Due to the experienced difficulty of flotation of thermally activated (at 500 degrees C) hydrotalcite metal-loaded particles, the application of various surfactants was studied. Continuous-flow laboratory runs certified also the effectiveness of this combined process of sorptive flotation, a promising innovative treatment technology.