Water pollution is a global problem threatening the entire biosphere and affecting the life of many millions of people around the world. Not only is water pollution one of the foremost global risk factors for illness, diseases and death, but it also contributes to the continuous reduction of the available drinkable water worldwide. Delivering valuable solutions, which are easy to implement and affordable, often remains a challenge. Here we review the current state-of-the-art of available technologies for water purification and discuss their field of application for heavy metal ion removal, as heavy metal ions are the most harmful and widespread contaminants. We consider each technology in the context of sustainability, a largely neglected key factor, which may actually play a pivotal role in the implementation of each technology in real applications, and we introduce a compact index, the Ranking Efficiency Product (REP), to evaluate the efficiency and ease of implementation of the various technologies in this broader perspective. Emerging technologies, for which a detailed quantitative analysis and assessment is not yet possible according to this methodology, either due to scarcity or inhomogeneity of data, are discussed in the final part of the manuscript.

Sustainable technologies for water purification from heavy metals: review and analysis

Physics of Radiology

Emerging natural and tailored materials for uranium-contaminated water treatment and environmental remediation

Dendrimers, mesoporous silicas and chitosan-based nanosorbents for the removal of heavy-metal ions: A review.

Uranium is known for its toxicity and has been a nuclear hazard. Its radioactive nature has made it a cause of lung and bone cancer. The uranium content in water bodies in several countries has surpassed the maximum permissible limits. In such regions of radioactive contamination of local soil and groundwater, the chemical toxicity of uranium has tremendously aggravated health concerns. Large scale loss of aquatic species has been witnessed due to uranium contamination. Governments have imposed regulations and set standards to limit the disposal of uranium in water bodies. Owing to its ability of fission, uranium simultaneously finds its application is nuclear energy generation. It is also used as a shield against radiation, as ammunition in military weaponry, as a counterweight for aircraft control surfaces, in radiotherapy and on-stream analysis of a wide range of minerals. With an objective to advance the understanding, this article covers the various techniques for the recovery of uranium along with a wide range of removal agents, considering the various factors that affect uranium uptake. The techniques contemplated upon include adsorption, membrane filtration, phytoremediation, reductive precipitation, microbiological methods and bio-precipitation. The isotherm and kinetic models used in adsorption have been stated and a comparative evaluation of the above listed techniques has also been done.

A review of potential remediation techniques for uranium(VI) ion retrieval from contaminated aqueous environment

Adsorption of uranium from aqueous solution by PAMAM dendron functionalized styrene divinylbenzene

Multi-walled carbon nanotubes (MWCNTs) were functionalized with diglycolamide (DGA) through chemical covalent route. The adsorption behavior of the DGA-functionalized-MWCNTs (DGA-MWCNTs) towards thorium from aqueous solution was studied under varying operating conditions of pH, concentration of thorium, DGA-MWCNTs dosages, contact time, and temperature. The effective range of pH for the removal of Th(IV) is 3.0–4.0. Kinetic data followed a pseudo-second-order model. The equilibrium data were correlated with the Langmuir, Freundlich, Dubinin-Radushkevich and Temkin models. The equilibrium data are best fitted with Langmuir model. The equilibrium Th(IV) sorption capacity was estimated to be 10.58 mg g−1 at 298 K. The standard enthalpy, entropy, and free energy of adsorption of the thorium with DGA-MWCNTs were calculated to be 8.952 kJ mol−1, 0.093 kJ mol−1 K−1 and -18.521 kJ mol−1 respectively at 298 K. The determined value of sticking probability (0.072) and observed kinetic and isotherm models reveal the chemical adsorption of thorium on DGA-MWCNTs.

Adsorptive removal of thorium from aqueous solution using diglycolamide functionalized multi-walled carbon nanotubes

Third generation poly(amido)amine (PAMAM) dendron was grown on the surface of styrene divinylbenzene (SDB) by divergent polymerization method. This new chelating resin (PAMAMG3-SDB) has been investigated in liquid–solid extraction of thorium. The effects of analytical parameters such as pH, contact time, concentration of thorium, resin dose and temperature on adsorption were investigated. Kinetic and isotherm studies of the adsorption were also carried out to understand the nature of adsorption of thorium on the chelating resin. Kinetic data followed a pseudo-second-order model and equilibrium data were best fitted with Langmuir model. The maximum adsorption capacity of thorium ions was determined to be 36.2 mg g−1 at 298 K. Thermodynamic parameters such as standard enthalpy, entropy, and free energy of adsorption of thorium on PAMAMG3-SDB were calculated as −10.498 kJ mol−1, 0.0493 kJ mol−1 K−1 and −25.208 kJ mol−1 respectively at 298 K from temperature dependent equilibrium data.

Removal of thorium from aqueous solution by adsorption using PAMAM dendron-functionalized styrene divinyl benzene

Study of Radon and Thoron exhalation from soil samples of different grain sizes.

This review deals with natural radioactivity variation along the southeast coast of Tamil Nadu for the past four decades (1974-2016). About 40 research works have been conducted along the coast since 1974 in various environmental matrices using a variety of experimental methods. For these measurements researchers are adopted different experimental methods. The measured gamma dose rate ranged from 30 to 8700 nGy/h. The mean specific activity of 238U, 232Th and 40K was found to be 58.8 ± 28.7, 465.2 ± 147.3 and 311.2 ± 27.8 Bq/kg, respectively. The calculated annual exposure rate ranged from 0.29 to 12.8 mSv/y with the mean value of 3.7 mSv/y which is above the global average of 2.4 mSv/y as reported by United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (Report to General Assembly, Annex B Exposures of the public and workers from various sources of radiation. United Nations, New York (2008)). Plant food items recorded low 210Po activities as compared to seafood organisms. Grain size, season and place of sampling have a decisive bearing on coastal radioactivity. Therefore, it is concluded from the review data that there is an appreciable elevation in background radiation level in the coastal region. This review suggests that new radiological surveys using improved methodology that cover the entire coastal stretch are needed.

K. Sivasubramanian

Papers

Adsorption of uranium from aqueous solution by PAMAM dendron functionalized styrene divinylbenzene

Adsorptive removal of thorium from aqueous solution using diglycolamide functionalized multi-walled carbon nanotubes

Removal of thorium from aqueous solution by adsorption using PAMAM dendron-functionalized styrene divinyl benzene

Study of Radon and Thoron exhalation from soil samples of different grain sizes.

A review on variation of natural radioactivity along the southeast coast of tamil nadu for the past 4 decades (1974-2016).