Sustainable Recovery of Secondary and Critical Raw Materials from Classified Mining Residues Using Mycorrhizal-Assisted Phytoextraction

In this work, mycorrhizal-assisted phytoextraction (MAP, Helianthus annuus–arbuscular mycorrhizal fungus Rhizophagus intraradices–Zn-volcanic ashes) was applied for the recovery of secondary and critical raw materials (SRMs and CRMs, respectively) from Joda West (Odisha, India) mine residues, within a novel multidisciplinary management strategy. Mine residues were preliminarily characterized by using advanced analytical techniques, and subsequently mapped, classified and selected using multispectral satellite Sentinel-2A images and cluster analysis. Selected mine residues were treated by MAP at laboratory scale, and the fate of several SRMs (e.g., Zn, Cr, As, Ni, Cu, Ca, Al, K, S, Rb, Fe, Mn) and CRMs (such as Ga, Ti, P, Ba and Sr) was investigated. Bioconcentration factors in shoots (BCS) and roots (BCR) and translocation factors (TF) were: 5.34(P) > BCS > 0.00(Al); 15.0(S) > BCR > 0.038(Ba); 9.28(Rb) > TF > 0.02(Ti). Results were used to predict MAP performance at larger scale, simulating a Vegetable Depuration Module (VDM) containing mine residues (1 m3). Estimated bio-extracting potential (BP) was in the range 2417 g/m3 (K) > BP> 0.14 g/m3 (As), suggesting the eventual subsequent recovery of SRMs and CRMs by hydrometallurgical techniques, with final purification by selective electrodeposition, as a viable and cost-effective option. The results are promising for MAP application at larger scale, within a circular economy-based approach.

Natural Fungal Endophytes From Noccaea caerulescens Mediate Neutral to Positive Effects on Plant Biomass, Mineral Nutrition and Zn Phytoextraction

Phytoextraction using hyperaccumulating plants is a method for the remediation of soils contaminated with trace elements (TEs). As a strategy for improvement, the concept of fungal-assisted phytoextraction has emerged in the last decade. However, the role played by fungal endophytes of hyperaccumulating plants in phytoextraction is poorly studied. Here, fungal endophytes isolated from calamine or non-metalliferous populations of the Cd/Zn hyperaccumulator Noccaea caerulescens were tested for their growth promotion abilities affecting the host plant. Plants were inoculated with seven different isolates and grown for 2 months in trace element (TE)-contaminated soil. The outcomes of the interactions between N. caerulescens and its native strains ranged from neutral to beneficial. Among the strains, Alternaria thlaspis and Metapochonia rubescens, respectively, isolated from the roots of a non-metallicolous and a calamine population of N. caerulescens, respectively, exhibited the most promising abilities to enhance the Zn phytoextraction potential of N. caerulescens related to a significant increase of the plant biomass. These strains significantly increased the root elemental composition, particularly in the case of K, P, and S, suggesting an improvement of the plant nutrition. Results obtained in this study provide new insights into the relevance of microbial-assisted phytoextraction approaches in the case of hyperaccumulating plants.

PHYTOREMEDIATION OF URANIUM TAILINGS: ROLE OF CHELATORS IN TRIGGERING URANIUM ACCUMULATION IN WHEAT

Chelator-assisted phytoextraction has been proposed as a potential tool for phytoremediation of uranium contaminated tailings. The purpose of the present investigation was to test the efficiency of the four various chelators namely, citric acid (CA), oxalic acid (OA), NTA and EDTA and to screen out the most effective chelator with promising concentration of it in increasing the U uptake and accumulation for phytoremedial programmes. Three kilograms of mixture (25:75; tailing: garden soil) was filled in the earthen pots. Treatment pots were prepared by applying- 0.1, 0.5, 2.5 and 12.5 mmol kg-1 concentrations of each of the chelator (CA, OA, NTA and EDTA). Optimum concentrations of the chelators were recorded considering biomass production, tolerance index and U uptake. Each chelator produced severe toxicity symptoms at 12.5 mmol kg-1 treatment level. Lowest depression in respect of growth was observed with NTA while OA and CA were proved less toxic than EDTA. Highest inhibition was recorded in EDTA treatments at respective levels. U uptake and accumulation was concentration dependent for each of the chelator amendment. Maximum U uptake (3.4-fold) in the roots occurred at 2.5 mmol kg-1 of CA while NTA proved to be the weakest for the same purpose. Not with standing, EDTA and NTA are stronger complexion agents than CA but in contrary, the use of CA proved beneficial in U tailing phytoremediation in the present investigation. The growth of the wheat plants was affected by each of the chelator, which in general follows the order: NTA ? OA ? CA ? EDTA, whereas the order for U accumulation was recorded as- CA > EDTA > OA > NTA. On the basis of this study it can be suggested that the use CA over EDTA is better, as it is easily biodegradable, less toxic and has lower leaching risk..