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Hydrometallurgical approaches have been successfully employed for metal separation and recovery from various types of waste materials. Therefore, hydrometallurgy is a promising technology for metal recovery and the removal of potentially toxic heavy metals found in industrial sludge. However, a comprehensive review that focuses on the heavy metal recovery from industrial sludge using hydrometallurgical approaches has not been conducted in the recent past. The present review discusses the capacity of hydrometallurgical techniques in recovering heavy metals sourced from different types of industrial sludges, highlighting recent scientific findings. Hydrometallurgical approaches primarily consist of three process stages: metal dissolution, concentration and purification, and metal recovery. The chemical characteristics of industrial sludge, including the type, concentration and speciation of heavy metals, directly impact selection of the best recovery method. Solvent extraction, ion-exchange, and adsorption are the major techniques employed in concentration and purification, whereas electrodeposition and precipitation are the main methods used in metals recovery. Future research should focus on the development of more efficient and environmentally-friendly methods for metal dissolution from industrial sludges contaminated with multiple metals, while increasing selectivity and energy use efficiency in the concentration and purification, and recovery steps.

Salinity and acidity have affected several hundred million hectares of land throughout the globe which poses a major threat to global food security and biodiversity. Application of organic amendments for salt-affected soils has been identified as one of the most effective ways to mitigate salinity-induced problems and considered as a green technique offering twin benefits of waste load reduction and land reclamation. However, studies on reclaiming acidic-salt affected soils are limited. Therefore, this study aimed to determine the reclamation potential of biochars and organic amendments involving Gliricidia sepium biochar produced at 300 °C, 500 °C, and 700 °C, green waste compost, and municipal sewage sludge at three different amendment ratios, 1.0%, 2.5% and 5.0%. The incubation experiment was conducted for a 4-month period with different amendment ratios applied to the coastal acidic-salt affected soil. Subsamples were extracted from incubation pots after 1 and 4 months and analyzed for soil chemical parameters (pH, EC, NO3−, PO43−, total organic carbon, cation exchange capacity, sodium adsorption ratio, exchangeable sodium percentage) and microbial enzyme activity (catalase activity, and acid- and alkaline phosphatase activity). All organic amendments demonstrated enhancement of the soil properties in a significant manner. However, increasing incubation time and amendment ratio increase the changes of soil parameters by a great percentage. Therefore, the maximum amendment ratio of 5.0% and 4 months of incubation period rendered a significant improvement in the reclamation of acidic-salt affected soil. However, the biochar produced at 500 °C contributed the maximum towards the improved physicochemical and biochemical profile of acidic-salt affected soil, making it the most promising organic amendment for the reclamation of acidic-salt affected soil. The overall reclamation efficiency of organic amendments registered the following order of variation: 700 BC

This review focuses on existing technologies for carcass and corpse disposal and potential alternative treatment strategies. Furthermore, key issues related to these treatments (e.g., carcass and corpse disposal events, available methods, performances, and limitations) are addressed in conjunction with associated environmental impacts. Simultaneously, various treatment technologies have been evaluated to provide insights into the adsorptive removal of specific pollutants derived from carcass disposal and management. In this regard, it has been proposed that a low-cost pollutant sorbent may be utilized, namely, biochar. Biochar has demonstrated the ability to remove (in)organic pollutants and excess nutrients from soils and waters; thus, we identify possible biochar uses for soil and water remediation at carcass and corpse disposal sites. To date, however, little emphasis has been placed on potential biochar use to manage such disposal sites. We highlight the need for strategic efforts to accurately assess biochar effectiveness when applied towards the remediation of complex pollutants produced and circulated within carcass and corpse burial systems. Graphical Abstract

The contamination of natural resources by hexavalent chromium (Cr(VI)) originating from natural and anthropogenic activities is a serious environmental concern. Although many articles on chromium remediation have been published, a comprehensive understanding of the mechanisms involved in remediation with different sorbents is not yet available. In this systematic review, the performance and applicability of several adsorptive materials for Cr(VI) removal from aqueous media are discussed, along with a detailed analysis of the mechanisms involved. Statistical analysis is applied to compare the efficacies of different adsorbents, while a similar approach is used to determine the effects of sorbent properties and experimental conditions on the adsorption capacity. A detailed analysis of the factors involved in fixed-bed column studies is also presented. A suitable desorption approach to the regeneration of the spent adsorbent and its adsorption performance in reuse is also examined. Among the different sorbents, nanoparticles and mineral-doped biochar were found to be the most effective sorbents, while the adsorption was higher at low pH (~4.0) than that at intermediate pH (6-8). Contrary to our expectation, adsorption was high for sorbents with low specific surface areas, suggesting that the adsorption of Cr(VI) is largely influenced by the chemical properties of the sorbents. The optimum adsorption in fixed-bed column systems is obtained at a lower Cr(VI) ion concentration, a lower influent flow rate, and a higher bed height. Since most of the studies reviewed herein were merely experimental and utilized ideal conditions with the presence of a single contaminant, i.e. Cr(VI) in water, further studies on adsorption dynamics with the presence of other interfering ions are suggested. This review is promising for the further development of Cr(VI) removal strategies and closes the research gaps pertaining to their challenges.

Purpose This study was conducted to evaluate the synergistic effects of organic amendments and soil water status on trace metal release from serpentine soil. Materials and methods Two organic amendments, dendro-biochar (BC) and municipal solid waste compost (CM), were added to serpentine soil at four different ratios, specifically 2.5:0.0, 2.5:1.0, 2.5:2.5, and 2.5:5.0% (w/w). Along with the control (with no organic amendments), each soil treatment was incubated separately under saturated point (SP) and field capacity (FC) water content for 10 days. Subsamples were obtained from each treatment to analyze the bioavailable trace metal concentration and related edaphic parameters, namely total organic carbon (TOC), nitrate (NO3−), phosphate (PO43−), and cation exchange capacity (CEC). Then, the soil solution was eluded from each treatment and incubated for 10 days under permanent wilting point (PW). Furthermore, a seed germination test was performed under the different treatments. Results and discussion Significant reductions (p

Open dumping of municipal solid waste is a common method of waste disposal in developing countries, thus leading to pollution by gaseous emissions and landfill leachate discharge. Biochar, a carbonaceous material produced from any biomass, is a means to transform municipal solid waste into a value-added product, which can be used for resources recovery and for contaminant mitigation. This review presents the production of biochar from municipal solid waste. Biochar from municipal solid waste has various properties depending on the production technology. We describe the use of biochar as a green adsorbent for leachate treatment and as a permeable reactive barrier material to reduce contamination. Furthermore, biochar can be used as a cover material to reduce odors.

Traditional methods of restoring E-waste contaminated sites via typical techniques such as physical treatment, subsequent excavating or dredging after disposal and chemical treatment, and application of chemical amendments or techniques involve exorbitant cost. Therefore developing of new low-cost and environment-friendly methods for removal of contaminants from E-waste contaminated sites is a rising global concern, where biological treatment, particularly phyto/bioremediation, plays a significant role. Phytoremediation, which utilizes plant to accumulate and store and/or degrade pollutants from the soil is considered as an extremely appealing method that could be employed effectively for in-site remediation of trace metals and organic pollutants. Therefore this chapter will extensively discuss the applicability of phytoremediation to remediate E-waste contaminated sites.

In this paper, we investigate the release of heavy metals from sludge produced from an electrical industry using both organic and inorganic acids. Single and sequential extractions were conducted to assess heavy metals in different phases of the sludge. Metal release from sludge was investigated in the presence of three inorganic acids (nitric, sulfuric, and phosphoric) and three organic acids (acetic, malic, and citric) at concentrations ranging from 0.1 to 2.0 mol L−1. Sequential extraction indicated the presence of Cu primarily in the carbonate fraction, Pb in the residual fraction, and Ni in the FeMn oxide fraction. The cumulative release rates of heavy metals (i.e., Pb, Cu, and Ni) by 1.0 mol L−1 of acid increased with the use of the following acids in the order of: malic < sulfuric < acetic < phosphoric < citric < nitric. Acetic acid exhibited the highest release of Cu, at a rate of 72.62 × 10−11 mol m−2 s−1 at pH 1, and malic acid drove the release of Pb at a maximum rate of 3.90 × 10−11 mol m−2 s−1. Meanwhile, nitric acid provided the maximum rate of Ni release (0.23 × 10−11 mol m−2 s−1) at pH 1. The high rate of metal release by organic acids is explained through ligand-promoted mechanisms that enhance the release of metal ions from the sludge. The results from our study emphasize that an understanding of the metal release mechanism is key to selecting the optimal acid for the maximum recovery of heavy metals

Environmental contamination by pharmaceutical and personal care products (PPCPs) is a worldwide concern. Although reported concentrations are generally low, a large numbers of PPCPs with diverse chemical natures have been detected in soil, water, and aquatic environments, and most of them can persist in the environment for long time posing detrimental effects on human health, biota, or other significant environment aspects. Several techniques such as bioremediation, ozonation, electrochemical separation technologies, and physicochemical treatments including coagulation, volatilization, sorption, sedimentation have been used to remediate PPCPs contaminated sites. This chapter provides a comprehensive overview of sorptive removal techniques of PPCPs and the mechanism of interaction. Until now, various sorbents including activated carbon, biochar, agricultural solid waste, industrial by-products, natural clay minerals, and biosorbents have been examined to remove PPCPs in water and wastewater. The diverse chemical nature and specific properties of PPCPs make the sorption process more complex in the natural environment. Hence, research interest needs to be focused on novel sorbents which are suitable for natural environment conditions. Moreover, specific properties of water/wastewater such as pH, ionic strength, other contaminants, and temperature should be considered for the selection of proper sorbent.

The transformation of trace metals (TMs) in natural environmental systems has created significant concerns in recent decades. Ultramafic environments lead to potential risks to the agricultural products and, subsequently, to human health. This unique review presents geochemistry of ultramafic soils, TM fractionation (i.e. sequential and single extraction techniques), TM uptake and accumulation mechanisms of ultramafic flora, and ultramafic-associated health risks to human and agricultural crops. Ultramafic soils contain high levels of TMs (i.e. Cr, Ni, Mn, and Co) and have a low Ca:Mg ratio together with deficiencies in essential macronutrients required for the growth of crops. Even though a higher portion of TMs bind with the residual fraction of ultramafic soils, environmental changes (i.e. natural or anthropogenic) may increase the levels of TMs in the bioavailable or extractable fractions of ultramafic soils. Extremophile plants that have evolved to thrive in ultramafic soils present clear examples of evolutionary adaptations to TM resistance. The release of TMs into water sources and accumulation in food crops in and around ultramafic localities increases health risks for humans. Therefore, more focused investigations need to be implemented to understand the mechanisms related to the mobility and bioavailability of TMs in different ultramafic environments. Research gaps and directions for future studies are also discussed in this review. Lastly, we consider the importance of characterizing terrestrial ultramafic soil and its effect on crop plants in the context of multi-decadal plans by NASA and other space agencies to establish human colonies on Mars. Keywords: Soil contamination, Geochemistry, Trace elements, Bioaccumulation, Translocation, Extremophytes

Municipal solid waste has become a hassle in many developing countries due to haphazard disposing to open dumpsites, which has zero management. This way of disposing the waste has negative impacts in the environment that can directly contribute to the climate changes and atmospheric pollution through greenhouse gas and volatile organic compound emission and water and soil pollution via landfill leachate as well. Biochar, a carbonaceous material produced by limited or no oxygen pyrolysis of biomass is an emerging efficient substitute for activated carbon. Its production utilizes different feedstock including municipal solid wastes, which is the “greener” approach of transforming the existing municipal waste into a value added product that can be used in contaminant mitigation and resource recovery by using it as an adsorbent and as a hybrid with soil for better plant growth. The long term benefits of these biochar additions to soil and water can be manifold and potential as an improved nutrient retention and availability to plant growth; this gives the impetus of having the “greener transformation” from municipal wastes to biochar. This chapter outlines the ways of production of biochar derived from municipal solid waste, its significance as an adsorbents and its promising potential in landfill cover, leachate treatment and for permeable reactive barriers.

Biochar has recently become an interesting option for soil management in terms of nutrients depleted lands, which is now emerging as an increasing global concern. Since biochar is derived from biomass, they are high in carbon and may contain a range of plant macro- and micronutrients. In addition, the physical microstructure of biochar may crucially influence the role of biochar on plant nutrient uptake determining access to mineralized elements by soil solution, microorganisms, and plant roots. The beneficial use of biochar as a soil amendment in terms of increased crop yield and improved soil quality has been reported. This book chapter extensively discusses the influential nutrients in biochars and their effects on plant nutrient uptake. Further, alteration of the mechanism of nutrient uptake via biochar modification and the effect on nutrient transformation in soil have been reviewed. Biochar impacts on nutrient uptake by different plants under different environmental and soil conditions are not fully understood yet. This chapter will provide insights for future research directions in order to establish an effective biochar-plant nutrient interaction.

Soil quality degradation is one of the most widespread phenomena for declining agricultural productivity throughout the world. It has been estimated that more than 40% of agricultural lands have been already become marginal due to mismanagement of soil. Biochar is a carbon rich product of a thermochemical conversion of biomass to be recognized as a beneficial soil amendment. It is not a novel soil amendment and history goes back to Mayan civilization called “Terra preta” soil. Due to the high fertility of these Amazon basin soils, many researchers in the world were interested in properties and application of biochar. This review gives an overview of agricultural benefits of biochar as a soil amendment. However, still there are many pros and cons of the application of biochar and this article will highlight the importance of further researches on the application of biochar as a soil amendment.