Optimization of desorption parameters using response surface methodology for enhanced recovery of arsenic from spent reclaimable activated carbon: Eco-friendly and sorbent sustainability approach.

Desorption and adsorbent regeneration are imperative factors that are required to be taken into account when designing the adsorption system. From the environmental, economic, and practical points of view, regeneration is necessary for evaluating the efficiency and sustainability of synthesized adsorbents. However, no study has investigated the optimization of arsenic species desorption from spent adsorbents and their regeneration ability for reuse as well as safe disposal. This study aims to investigate the desorption ability of arsenic ions adsorbed on hybrid granular activated carbon and the optimization of the independent factors influencing the efficient recovery of arsenic species from the spent activated carbon using central composite design of the response surface methodology. The activated carbon before the sorption process and after the adsorption-desorption of arsenic ions have been characterized using SEM-EDX, FTIR, and TEM. The study found that all the investigated independent desorption variables greatly influence the retrievability of arsenic ions from the spent activated carbon. Using the desirability function for the optimization of the independent factors as a function of desorption efficiency, the optimum experimental conditions were solution pH of 2.00, eluent concentration of 0.10 M, and temperature of 26.63 ℃, which gave maximum arsenic ions recovery efficiency of 91 %. The validation of the quadratic model using laboratory confirmatory experiments gave an optimum arsenic ions desorption efficiency of 97 %. Therefore, the study reveals that the application of the central composite design of the response surface methodology led to the development of an accurate and valid quadratic model, which was utilized in the enhanced optimization of arsenic ions recovery from the spent reclaimable activated carbon. More so, the desorption isotherm and kinetic data of arsenic were well correlated with the Langmuir and the pseudo-second-order models, while the thermodynamics studies indicated that arsenic ions desorption process was feasible, endothermic, and spontaneous.

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.

Artisanal and small-scale mining in Tanzania and health implications: A policy perspective.

The mineral sector, especially its small-scale subsector, has become significant in the emerging economies of the Global South. Tanzania is the focus of this policy exposition paper because, aside from Ghana and South Africa, Tanzania is ranked 4th in Africa in terms of its mineral deposits and small-scale mining activities. The focus is also on artisanal and small-scale mining (ASM) because ASM operations have significantly increased in recent times across this mineral-rich country of East Africa. This is done against a negative backdrop-labelling of ASM as unsustainable, environmentally unfriendly, inefficient, and illegal. Tanzania has made some progress to respond to some of the challenges in the mining sector to improve the micro and macroeconomics of the country. Some areas remain challenging including the lack of proper environmental health education for the ASM miners; the lack of clear national-level policies to guide health-related matters in the ASM subsector, and the small capital investment of the ASM subsector to support healthy mining practices. The details related to the persistence of these challenges are not well known, particularly those that pertain to policymaking. This article attempts to evaluate the policy environment of the ASM subsector in Tanzania and propose appropriate actions for the future of mineral resource policymaking in Tanzania.

A comprehensive review on the decontamination of lead(ii) from water and wastewater by low-cost biosorbents.

The disadvantages of conventional methods in water and wastewater management including the demand for high energy consumption, the creation of secondary toxic sludge, and operation cost are much too high for developing countries. However, adsorption using low-cost biosorbents is the most efficient non-conventional technique for heavy metals removal. The high adsorption capacities, cost-effectiveness, and the abundance of agricultural waste materials in nature are the important parameters that explain why these biosorbents are economical for heavy metals removal. The present investigation sought to review the biosorption of lead [Pb(ii)] onto low-cost biosorbents to understand their adsorption mechanism. The review shows that biosorption using low-cost biosorbents is eco-friendly, cost-effective, and is a simple technique for water and wastewater treatment containing lead(ii) ions. The batch biosorption tests carried out in most studies show that Pb(ii) biosorption by the low-cost biosorbents is dependent on biosorption variables such as pH of the aqueous solution, contact time, biosorbent dose, Pb(ii) initial concentration, and temperature. Furthermore, batch equilibrium data have been explored in many studies by evaluating the kinetics, isothermal and thermodynamic variables. Most of the studies on the adsorptive removal of Pb(ii) were found to follow the pseudo-second kinetic and Langmuir isotherm models with the thermodynamics variables suggesting the feasibility and spontaneous nature of Pb(ii) sequestration. However, gaps exist to increase biosorption ability, economic feasibility, optimization of the biosorption system, and desorption and regeneration of the used agricultural biosorbents.

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.

An extensive review on chromium (vi) removal using natural and agricultural wastes materials as alternative biosorbents.

Several conventional techniques for heavy metals decontamination for instance ion exchange, evaporation, precipitation and electroplating have been utilized in preceding years. Though these techniques have some drawbacks, adsorption using low-cost biosorbents is environmentally friendly. In this study, the potential of several natural and agricultural wastes as economical biosorbents for the reduction of Cr(VI) ions from polluted water has been reviewed. The application of adsorption models, as well as the impact of adsorption factors on heavy metals eradication, has been considered in this review. The study revealed that efficient reduction of Cr(VI) from water and wastewaters is highly dependent on the pH of the solution, shaking time, adsorbent type, initial concentration and temperature. The review of the relevant literature indicates that the maximum removal efficiency of Cr(VI) using the various low-cost adsorbents ranged from 50.0-100.0% with optimum pH and contact time ranging from 2.0-6.0 and 30.0-180.0 min, respectively at room temperature (25.0 °C). Furthermore, considering all the studies reviewed, the pseudo-second-kinetics and Langmuir isotherm are the dominant models that best described the Cr(VI) equilibrium data. The thermodynamic parameters suggested that the biosorption of Cr(VI) on the biosorbents was spontaneous, realistic and endothermic at the temperature range of 30.0-45.0 °C. It is found that the natural and agricultural wastes as cheap biosorbents are feasible replacements to commercial activated carbons for metal-contaminated water treatment. However, gaps have been identified to improve applicability, regeneration, reuse and safe discarding of the laden adsorbents, optimization and commercialization of suitable agricultural adsorbents.