Experimental investigations of arsenic adsorption from contaminated water using chemically activated hematite (Fe2O3) iron ore

Adsorption and desorption processes of toxic heavy metals, regeneration and reusability of spent adsorbents: Economic and environmental sustainability approach

A growing number of variables, including rising population, water scarcity, growth in the economy, and the existence of harmful heavy metals in the water supply, are contributing to the increased demand for wastewater treatment on a global scale. One of the innovative water treatment technologies is the adsorptive removal of heavy metals through the application of natural and engineered adsorbents. However, adsorption currently has setbacks that prevent its wider application for heavy metals sequestration from aquatic environments using various adsorbents, including difficulty in selecting suitable desorption eluent to recover adsorbed heavy metals and regeneration techniques to recycle the spent adsorbents for further use and safe disposal. Therefore, the recovery of adsorbed heavy metal ions and the ability to reuse the spent adsorbents is one of the economic and environmental sustainability approaches. This study presents a state-of-the-art critical review of different desorption agents that could be used to retrieve heavy metals and regenerate the spent adsorbents for further adsorption-desorption processes. Additionally, an attempt was made to discuss and summarize some of the independent factors influencing heavy metals desorption, recovery, and adsorbent regeneration. Furthermore, isotherm and kinetic modeling have been summarized to provide insights into the adsorption-desorption mechanisms of heavy metals. Finally, the review provided future perspectives to provide room for researchers and industry players who are interested in heavy metals desorption, recovery, and spent adsorbents recycling to reduce the high cost of adsorbents reproduction, minimize secondary waste generation, and thereby provide substantial economic and environmental benefits.

Adsorption and desorption ability of divalent mercury from an interactive bicomponent sorption system using hybrid granular activated carbon

The sequestration of heavy metals from multicomponent sorption media has become critical due to the noxious effects of heavy metals on the natural environment and subsequently on human health as well as all life forms. The abatement of heavy metals using bio-adsorbents is one of the efficient and affordable approaches for treating water and wastewater. Therefore, the interactive effect of arsenic [As(III)] ions on the sorption and desorption ability of mercury [Hg(II)] from a binary sorption system was conducted. More so, the impact of reaction time, solution pH, bio-adsorbent particle size, bio-adsorbent dose, initial mono-metal, and binary-metal concentration as well as reaction temperature on the individual and competitive sorption of Hg(II) was explored. The study showed that Hg(II) could be removed effectively from the single-component system and competitively from the aqueous phases by the bio-adsorbent in the coexistence of As(III) species in the bicomponent medium. The adsorptive detoxification of Hg(II) from the monocomponent and bicomponent sorption media showed dependence on all the studied adsorption parameters. The occurrence of As(III) species in the bicomponent sorption medium affected the decontamination of Hg(II) by the bio-adsorbent and the major interactive mechanism was found to be antagonism. The spent bio-adsorbent was effectively recycled using 0.10 M nitric (HNO3) and hydrochloric (HCl) acids solutions and the multi-regeneration cycles showed a high removal efficiency in each cycle. The first regeneration cycle was found to have the highest Hg(II) ions removal efficiencies of 92.31 and 86.88% for the monocomponent and bicomponent systems, respectively. Thus, the bio-adsorbent was found to be mechanically stable and reusable up to the 6.00 regeneration cycle. Therefore, this study concludes that the bio-adsorbent not only has a higher adsorption capacity but also a good recycling performance pointing to good industrial applications and economic prospects.

Removal of heavy metals from binary and multicomponent adsorption systems using various adsorbents - a systematic review

The ecosystem and human health are both significantly affected by the occurrence of potentially harmful heavy metals in the aquatic environment. In general, wastewater comprises an array of heavy metals, and the existence of other competing heavy metal ions might affect the adsorptive elimination of one heavy metal ion. Therefore, to fully comprehend the adsorbent's efficiency and practical applications, the abatement of heavy metals in multicomponent systems is important. In the current study, the multicomponent adsorption of heavy metals from different complex mixtures, such as binary, ternary, quaternary, and quinary solutions, utilizing various adsorbents are reviewed in detail. According to the systematic review, the adsorbents made from locally and naturally occurring materials, such as biomass, feedstocks, and industrial and agricultural waste, are effective and promising in removing heavy metals from complex water systems. The systematic study further discovered that numerous studies evaluate the adsorption characteristics of an adsorbent in a multicomponent system using various important independent adsorption parameters. These independent adsorption parameters include reaction time, solution pH, agitation speed, adsorbent dosage, initial metal ion concentration, ionic strength as well as reaction temperature, which were found to significantly affect the multicomponent sorption of heavy metals. Furthermore, through the application of the multicomponent adsorption isotherms, the competitive heavy metals sorption mechanisms were identified and characterized by three primary kinds of interactive effects including synergism, antagonism, and non-interaction. Despite the enormous amount of research and extensive data on the capability of different adsorbents, several significant drawbacks hinder adsorbents from being used practically and economically to remove heavy metal ions from multicomponent systems. As a result, the current systematic review provides insights and perspectives for further studies through the thorough and reliable analysis of the relevant literature on heavy metals removal from multicomponent systems.

Response surface optimization and modeling in heavy metal removal from wastewater-a critical review

The existence of hazardous heavy metals in aquatic settings causes health risks to humans, prompting researchers to devise effective methods for removing these pollutants from drinking water and wastewater. To obtain optimum removal efficiencies and sorption capacities of the contaminants on the sorbent materials, it is normally necessary to optimize the purification technology to attain the optimum value of the independent process variables. This review discusses the most current advancements in using various adsorbents for heavy metal remediation, as well as the modeling and optimization of the adsorption process independent factors by response surface methodology. The remarkable efficiency of the response surface methodology for the extraction of the various heavy metal ions from aqueous systems by various types of adsorbents is confirmed in this critical review. For the first time, this review also identifies several gaps in the optimization of adsorption process factors that need to be addressed. The comprehensive analysis and conclusions in this review should also be useful to industry players, engineers, environmentalists, scientists, and other motivated researchers interested in the use of the various adsorbents and optimization methods or tools in environmental pollution cleanup.

As(III, V) Uptake from Nanostructured Iron Oxides and Oxyhydroxides: The Complex Interplay between Sorbent Surface Chemistry and Arsenic Equilibria

Iron oxides/oxyhydroxides, namely maghemite, iron oxide-silica composite, akaganeite, and ferrihydrite, are studied for AsV and AsIII removal from water in the pH range 2-8. All sorbents were characterized for their structural, morphological, textural, and surface charge properties. The same experimental conditions for the batch tests permitted a direct comparison among the sorbents, particularly between the oxyhydroxides, known to be among the most promising As-removers but hardly compared in the literature. The tests revealed akaganeite to perform better in the whole pH range for AsV (max 89 mg g-1 at pH0 3) but to be also efficient toward AsIII (max 91 mg g-1 at pH0 3-8), for which the best sorbent was ferrihydrite (max 144 mg g-1 at pH0 8). Moreover, the study of the sorbents' surface chemistry under contact with arsenic and arsenic-free solutions allowed the understanding of its role in the arsenic uptake through electrophoretic light scattering and pH measurements. Indeed, the sorbent's ability to modify the starting pH was a crucial step in determining the removal of performances. The AsV initial concentration, contact time, ionic strength, and presence of competitors were also studied for akaganeite, the most promising remover, at pH0 3 and 8 to deepen the uptake mechanism.

Removal of arsenate using graphene oxide-iron modified clinoptilolite-based composites: adsorption kinetic and column study

In this study, graphene oxide (GO), iron modified clinoptilolite (FeZ), and composites of GO-FeZ (GOFeZA and GOFeZB) were synthesized and characterized using SEM, EDS, XRF, FTIR, and pHpzc. The arsenate uptake on composites of GOFeZA and GOFeZB was examined by both kinetic and column studies. The adsorption capacity increases with the increase of the initial arsenate concentration at equilibrium for both composites. At the initial arsenate concentration of 450 μg/L, the arsenate adsorption on GOFeZA and GOFeZB was 557.86 and 554.64 μg/g, respectively. Arsenate adsorption on both composites showed good compatibility with the pseudo second order kinetic model. The adsorption process was explained by the surface complexation or ion exchange and electrostatic attraction between GOFeZA or GOFeZB and arsenate ions in the aqueous solution due to the relatively low equilibrium time and fairly rapid adsorption of arsenate at the beginning of the process. The adsorption mechanism was confirmed by characterization studies performed after arsenate was loaded onto the composites. The fixed-bed column experiments showed that the increasing the flow rate of the arsenate solution through the column resulted in a decrease in empty bed contact time, breakthrough time, and volume of treated water. As a result of the continuous operation column study with regenerated GOFeZA, it was demonstrated that the regenerated GOFeZA has lower breakthrough time and volume of treated water compared to fresh GOFeZA.