Recently, there is a growing research interest in the applications and development of novel sustainable hydrogel materials in waste water treatment because of radically distinctive chemical and physical characteristics of hydrogels such as hydrophilicity, swell ability and modifiability to name a few. Hydrogels have exposed the hypernym functioning in the removal of a wide range of aqueous pollutants containing toxic dyes and heavy metal ions. A large amount of water gets incorporated in the three dimensional networks of hydrophilic structures of hydrogels. The prime objective of this review article is to render a presentation on the recent advances in the modifications of sodium alginate based hydrogels for the adsorptive removal of toxic pollutants. In addition, article also briefly gives the classification and properties of hydrogels and alginate.

Recycling is groundwork of the worldwide efforts to diminish the amount of plastics in waste. Mostly around 7.8-8.2 million tons of poorly-used plastics enter the oceans every year. Nonbiodegradable plastics settlements in landfills are uncertain, which hinders the production of land resources. Non-biodegradable plastic solid wastes, carbon dioxide, greenhouse gases, various air pollutants, cancerous polycyclic aromatic hydrocarbons and dioxins, released to the environment cause severe damage and harmfulness to the inhabitants. Due to the bio-degradability and renewability of biopolymers, petroleum-based plastics can be replaced with bio-based polymers in order to minimize the environmental risks. In this review article, bio-degradability of polymers has been discussed. The mechanisms of bio-recycling have been particularly emphasized in the present article.

et al., Graphite modified sodium alginate hydrogel composite for efficient removal of malachite green dye,

Energy-efficient metal recovery and separation processes from a mixture of valuable metals are vital to the metallurgy and recycling industries. Oxalate has been identified as a sustainable reagent that can provide both the desired selectivity and efficient leaching capabilities for a variety of mixed metals under mild reaction conditions. The oxalate process has a great potential to replace many of the existing metal recovery processes that use inorganic acids such as sulfuric, hydrochloric, and nitric acids. In this Review, the use of oxalate chemistry in four major metal recovery applications is discussed, namely, spent lithium-ion batteries, spent catalysts, valuable ores, and contaminated and unwanted waste streams. Recycling of critical and precious metals from spent lithium-ion batteries and catalysts has significant economic opportunities. For efficient metals recovery, reaction conditions (e.g., temperature, pH, time, and concentration), metal−oxalate complex formation, oxidation and reduction, and metal precipitation must all be well-understood. This Review provides an overview from articles and patents for a variety of metal recovery processes along with insights into future process development.

The demand for lithium-ion batteries (LiBs) is significantly increasing leading to a shortage in supply for critical metals, such as lithium and cobalt. Recycling LiCoO 2 cathodes can provide a secondary source for these critical metals, which are necessary raw materials for the synthesis of modern LiB cathodes, such as nickel manganese cobalt oxide (NMC). In this work, an environmentally friendly, closed-loop process for recovery and separation of lithium and cobalt from LiCoO 2 cathodes has been developed using oxalate chemistry. In this paper, oxalic acid and ammonium hydrogen oxalate are utilized as digestion reagents to extract lithium into the aqueous phase (Li 2 C 2 O 4 ) and precipitate cobalt oxalate (CoC 2 O 4 •2H 2 O) in the solid phase resulting in a low-temperature, cost-effective separation of these metals. A greencolored intermediate was identified as a Co(III)-oxalate complex; this complex further reduces and precipitates as a Co(II)-oxalate complex (CoC 2 O 4 •2H 2 O). The optimum acidity for digestion and metals separation using oxalate containing acids was a pH < 2.5. The minimum amount of oxalic acid required for digestion was determined in order to develop the most economical process with more than 97 wt % Li and Co recovery. The proposed process is an energy-efficient, cost-effective, environmentally friendly process for recovering high-value, critical metals, such as lithium and cobalt from LiBs and other sources.