Fly ash-based geopolymers: an emerging sustainable solution for heavy metal remediation from aqueous medium

Background The water supplies are hindered because aquatic resources have constrained with natural and man-made pollution activities in terms of releasing huge amounts of contaminants from different point and non-point sources across the globe. The industries like metal plating, batteries, paint, fertilizers, tanneries, textile industries, dyeing industries, mining operations, and paper industries discharge their effluents into the environment directly or indirectly, and hence, they are considered as the key sources of heavy metals contamination in water resources. Heavy metals are inorganic, non-biodegradable, persistent, and having a tendency to get accumulated in biotic and abiotic components of environment as compared to organic pollutants. Some heavy metal cations, for example, mercury, arsenic, cadmium, zinc, lead, nickel, copper, and chromium, are carcinogenic in nature and so, lethal. There are growing health concerns due to toxic impacts of heavy metals on every genre of ecosystem. To deal with the bottleneck situation, it is highly imperative to search a feasible solution for heavy metal remediation in water in context of preventing amalgamation of noxious contaminants in food web. Different methods are exercised for the remediation of such impurities from its solutions. One method, i.e. adsorption is found to be the simplest, economical, efficient, and eco-friendly in this context. Main body Geopolymers exhibit heterogeneous amorphous microstructure and wide surface area. The compatibility for depollution and the performance of these materials mainly depend upon their preparation methods, composition, and microstructure. Fly ash-based geopolymer may serve as a better alternate to various cost-effective adsorbents and it will be a proven environmentally viable, waste to money solution by consuming heaps of fly ash waste for the adsorbent modified by using fly ash. The possible utilization of wastes from several industries is a matter of concerned sustainability benefits. This study shows that fly ash-based geopolymers have the potential to cope up with the problems and risk factors associated with the fly ash waste management and it would be the utmost scientific panacea in the field of removing toxins from aqueous medium and maintain environmental health in the future. Short conclusions The literature available in different databases is very limited pertaining to heavy metal remediation using fly ash-based geopolymers. Keeping all the factors in mind, this article is an attempt to summarize relevant informations related to work done on fly ash-based geopolymers for treating aqueous solutions comprising heavy metals.

Advances in Heavy Metal Bioremediation: An Overview

The pollution of toxic heavy metals is considered one of the most important environmental issues which has accelerated dramatically due to changing industrial activities. This review focuses on the most common methods, strategies, and biological approaches of heavy metal bioremediation. Also, it provides a general overview of the role of microorganisms in the bioremediation of heavy metals in polluted environments. Advanced methods of heavy metal remediation include physicochemical and biological methods; the latter can be further classified into in situ and ex situ bioremediation. The in situ process includes bioventing, biosparging, biostimulation, bioaugmentation, and phytoremediation. Ex situ bioremediation includes land farming, composting, biopiles, and bioreactors. Bioremediation uses naturally occurring microorganisms such as Pseudomonas, Sphingomonas, Rhodococcus, Alcaligenes, and Mycobacterium. Generally, bioremediation is of very less effort, less labor intensive, cheap, ecofriendly, sustainable, and relatively easy to implement. Most of the disadvantages of bioremediation relate to the slowness and time-consumption; furthermore, the products of biodegradation sometimes become more toxic than the original compound. The performance evaluation of bioremediation might be difficult as it has no acceptable endpoint. There is a need for further studies to develop bioremediation technologies in order to find more biological solutions for bioremediation of heavy metal contamination from different environmental systems.

Sustainable robust green synthesis of nanoparticles from waste aquatic plants and its application in environmental remediation

Green synthesis of nanoparticles using natural materials is an emerging technique that fascinates the scientific community globally for the treatment of wastewater. In the present study, aquatic plants such as Piaropus crassipes (PC) and Lemna gibba (LG), were utilized to make low-cost nanoparticles, and its feasibility for the removal of Zn(II) ions was studied. The synthesized nano adsorbents were characterized by Scanning Electron Microscopy (SEM), Fourier Transform Infra-Red Spectroscopy (FTIR), Brunauer Emmett-Teller (BET) analysis, and Zeta potential analysis. The optimal conditions were evaluated by batch adsorption studies, to investigate the parameters suchas pH (2–7), adsorbent dosage (0.5–5 g/L), initial concentration (20–60 mg/L), and contact time (10–120 min) etc, respectively. The isotherm, and kinetic data results fit well with Langmuir, and pseudo-second order model. The anticipated monolayer adsorption capacity with respect to the PC, and LG was found to be 42.41 mg/g and 27.65 mg/g, respectively. Thermodynamic studies showed that the process is exothermic. The adsorption mechanism of PC/LG on Zn(II) exhibited surface complexation, ion exchange, and diffusion. Desorption studies were performed to analyze the recovery potential of Zn(II) ion. Hence, this article investigates the economic synthesis of green nanoparticles, and their potential utilization in heavy metal remediation.