Phosphonomethyl iminodiacetic acid functionalized metal organic framework supported PAN composite beads for selective removal of La(III) from wastewater: Adsorptive performance and column separation studies.

The rare earth elements being toxic in nature are being accumulated in water bodies as their industrial usage is growing exponentially, thus their efficient separation holds an immense significance. Herein, ligand functionalized metal organic framework (MOF), Phosphonomethyl iminodiacetic acid coordinated at Fe-BTC, was synthesized post-synthetically and incorporated subsequently in polyacrylonitrile polymer to prepare the composite beads via nonsolvent induced-phase-inversion technique for selective adsorption of La(III) from the wastewater in batch and dynamic column mode. XPS NMR, and FTIR were used to establish the interaction between functionalized ligand and unsaturated metal nodes of MOF. The adsorption capacity was 232.5 mg/g and 77.51 mg/g at 298 K of the functionalized MOF and composite beads respectively. Adsorption kinetics followed a pseudo-second order rate equation, and isotherm indicated the best fitting with Langmuir model. The dynamic behavior of the adsorption column packed with MOF/Polymer beads was fairly described by the Thomas model. The breakthrough time of 23.2 h could be attained with 12 cm of bed height and 10 ml/min of flow rate. These MOF/Polymer beads shown the selectivity of La over transitional metals were recycled over 5 times with about 15% loss of adsorption capacity. The findings provide suggestive insights of the potential use of functionalized MOF towards the separation of the rare earth element.

Valorisation of waste galvanizing dross: Emphasis on recovery of zinc with zero effluent strategy.

Galvanizing dross-a waste product from steel industries but it can be a potential secondary resource for zinc through urban mining and recycling. In this concern, a novel and scalable recycling route with zero effluent strategy is developed for the recovery of zinc from galvanizing dross as high grade zinc salts along with value-added products through hydrometallurgical processing. In particular, as-such dross block was leached in 9% (v/v) sulphuric acid medium, wherein strong hydrogen gas effervescence results in alleviating the pulverization and stirring requirements; which are material and energy intensive. Leached zinc is purified and recovered as high purity ZnSO4.(H2O/7H2O) and Zn3(PO4)2.4H2O through controlled crystallization and phosphate precipitation respectively; which find application in fertilizers and anti-corrosive paints. Temperature difference method was opted for the crystallization of zinc sulfate salts, wherein 70 °C and 30 °C were found to be stability range of crystallization of ZnSO4.H2O and ZnSO4.7H2O respectively. ZnSO4-H2O phase diagram is developed using Factsage calculations to corroborate crystallization study. Moreover, exhaustive thermodynamic analysis of Zn2+-PO43--H2O system at 303 K on precipitation of zinc phosphate using di-ammonium hydrogen phosphate (80-240 g/L) is conducted and the results reveal that with increasing pH (3-6), intermediate hydrogen phosphate species (H3PO4, H2PO4- and H2PO42-) decompose to produce stable PO43- ions leading to zinc phosphate precipitation. Impurity like Iron and supernatant solution left after crystallization are recovered as hydrated iron-calcium sulfate mixture and ammonium sulfate salt respectively. This explored route is economical and easily adaptable with zero effluents, therefore, transcends serious challenges in terms of energy requirement, scale-up and effluent generation.