Effect of coexisting metal ions on bio-precipitation of Cu2+ phosphate by Rahnella sp. LRP3 and its stability in soil

The phosphate precipitation of heavy metal induced by microorganisms plays an important role in immobilising heavy metal in soil. However, there is little knowledge about the effect of coexisting metal ions on the induction of Cu phosphate mineral and its stability. In this paper, the Cu phosphate precipitations, coexisting with Pb²⁺ or Ca²⁺ induced by strain LRP3, were characterised, and the stabilisation of the induced phosphate precipitates was also studied. The coexistence of Cu with Pb or Ca decreased the removal efficiency of Cu²⁺ by 17.18% and 9.78%, respectively, indicating the competitive adsorption between cations. Strain LRP3 could induce a new phosphate mineral of CuCa₁₀(PO₄)₇ when coexisting with Ca and also generate the phosphate minerals of Pb(H₂PO₄)₂ and Cu₃(PO₄)₂ when coexisting with Pb. The Cu-Ca coprecipitate could enhance the stability of Cu in dilute acid solution and soil with or without a plant, whiles the Cu-Pb one showed the opposite effect. Also, the Cu-induced phosphate precipitates were relatively stable and not easy to be absorbed by Pakchoi (Brassica rapa var. chinensis). The results showed that the influence of coexisting metal ions should be considered when phosphate mineralisation technology is used to immobilise heavy metals in the environment.

Recycling of REMS and removal of toxic metals from fluorescent and CRT waste: a review

Fluorescent lamp and cathode ray tube (CRT) waste considered as hazardous waste by commission of European communities and resource conservation and recovery act (RCRA). Due to the presence of mercury and lead in fluorescent waste and cathode ray tube waste, it is highly toxic for environment. Simultaneously, these wastes are also a vital source of different rare earth elements (REEs) such as Y, Eu, Ce, Tb and La. REEs are the most critical resources in the development of both traditional and high-tech industries all over the world. In order to prevent the misuse of natural resources, recycling of REEs from fluorescent and CRT waste is an effective step for accelerating the sustainable use of resources and protect environmental pollution from mining. So, recovery of REEs as well as removal of contaminated hazardous metals such as Hg and Pb from waste is a challenging task. Many researchers in the last few years focused on the development of different process such as solvent extraction, selective leaching, and precipitation for recovery of rare earth elements as well as the removal of toxic metal from waste. Particularly recoveries of yttrium and europium metals are the main interest of many researchers due to huge application in CFL bulbs and CRT tubes. Selective leaching of Y and Eu can be obtained in dilute acid solution with moderate temperature. Dissolution of Pb in leaching process can be avoided by leaching with H2SO4 as it forms insoluble sulfate. While coming to solvent extraction, three major classes of conventional extractantshavebeen used for extraction of REEs such as cation exchanger, solvating extractants and anion exchangers. The use of ionic liquids instead of conventional extractantsismore interesting in modern research because of their high thermal stability, nontoxic and high extraction ability. They are used for effective recovery of REEs from e-waste.

Nutritional Evaluation of Millet Plants Grown in Soils Fertilized With Organic Wastes From Different Sources

The losses of essential elements to crops make necessary to correct soil fertility to meet the nutritional requirements of plants, which can be achieved by increasing soil organic matter. The objective of this work was to evaluate the leaf nutritional conditions of millet plants grown in soils fertilized with organic wastes from different sources at different rates. Organic matter can make the soil more productive and suitable to agricultural crops. A randomized block experimental design with a 4 × 2 factorial arrangement was used with four replications, consisting of 32 experimental units. The treatments consisted of four organic matter sources (swine manure, sewage sludge, bovine manure, and poultry litter), and two organic matter rates (20% and 40% of the pot volume). Boron extraction was performed by dry digestion—the organic matter of the plant tissue was incinerated in an electric muffle furnace at 450-550 ºC, and the inorganic residue (ash) was dissolved in a dilute acid solution. N, K, Ca, Mg, S, Fe, Cu, Mn, and Zn was extracted through wet digestion—the organic matter of the leaf tissue was oxidized by concentrated mineral acids and by heat. N, P, S, B, Ca, Mg, Cu, Fe, Mn, and Zn was determined by spectrophotometry. K was determined by flame photometry. All macro and micronutrient contents in the millet leaves, and biometric parameters of the millet panicle were affected by the organic matter sources, organic matter rates, and the interaction between them.