Search

This month's column is Part 2 of a contribution from my daughter Glenna, who recently completed her PhD studies in Environmental Science from the University of Copenhagen in Denmark. Her article explores the current landscape of global critical raw materials (CRM) trends in research and the applications of atomic spectroscopy (AS), including inductively coupled plasma-mass spectrometry (ICP-MS), inductively coupled plasma-optical emission spectrometry (ICP-OES), and X-ray analytical techniques in their identification of diverse industrial and environmental media, which have been essential in method validation and quantification of CRMs in complex matrices presenting high risks of interference. Some important examples to be presented include rare earth elements (REEs) in water leaching purification (WLP) residues that co-occur with radioactive materials; REEs and other metals in acid mine drainage (AMD) environments; REEs in coal combustion (fly ash) residues; arsenic (As) from groundwater treatment sediment; and platinum-group elements (PGEs) from sewage sludge. The article also classifies the different techniques in use at each stage of the CRM recovery train, investigates present challenges to each analytical method, and discusses the problem-solving tools used., - Rob Thomas, Column Editor Part 1 of this article focused on the overview of critical raw materials (CRMs), the global context for sustainable sourcing of CRMs, and the recent […]

Edited by Marcus DuBois King Oxford University Press, 2020, 268 pages, $28.19, ISBN: 9780197552636 The Middle East and North Africa (MENA) can be considered as one of the most water-stressed [...]

Context. Organic fertilisation may increase soil phosphorus (P) availability and increase risk of P loss to groundwater. Aims. To understand the effect of continuously applying organic fertilisers on formation of P fractions. Methods. A field experiment was conducted to investigate the effect of different fertilisation (CF, chemical fertiliser; COF, cow dung compost with chemical fertiliser; POF, pig manure compost with chemical fertiliser) on different soil P fractions for five growing seasons. Key results. Compared with CF, the COF and POF treatments had significantly higher total P and available P contents in each season. The COF treatment showed the highest concentration of NaOH-[P.sub.i]; however, POF showed the highest concentration of HCl-[P.sub.i] in all seasons. There were significant positive correlations between concentrations of total P (r = 0.863, P = 0.001), available P (r = 0.590, P = 0.006), each P fraction (r = 0.447 to 0.862, P = 0.048 to 0.001) and organic carbon concentration. Concentrations of total P (r = -0.473, P = 0.035), available P (r = -0.589, P = 0.006) and each P fraction (except HCl-[P.sub.i]) (r = -0.71 1 to -0.476, P = 0.001 to 0.034) showed significant negative correlations with soil pH. Available P concentration showed the highest correlation with concentrations of residual P (r = 0.665, P = 0.007), HCl-[P.sub.i] (r = 0.413, P = 0.126) and NaOH-[P.sub.i] (r = 0.282, P = 0.309) in CF, COF and POF treatments, respectively. Conclusions. Continuous application of organic fertiliser can significantly improve P availability through impacting distribution of P fractions. Implications. Further studies are needed to establish the release risk of each P fraction in soils. Keywords: correlation, field experiment, five growing seasons, organic fertiliser, P availability, P transformation, soil P fraction, soil pH and organic C., Introduction Phosphorus (P) is a key macronutrient for the growth of plants. An increasing amount of P fertilisers is being applied to soil to help provide enough food for the [...]

The regolith-hosted rare earth element (REE) deposits in the Nanling Mountain Range, South China, are the most important source of heavy REE (HREE) in the world. A perplexing thing is that only a few of these deposits are relatively enriched in HREE and most of them are actually light REE (LREE)-enriched, although they are all originated from the granitic bedrocks with similar HREE concentrations. This is supposed to be related to the redistribution of REE in the weathered bedrocks due to groundwater-rock interaction, however, it remains enigmatic how REEs are mobilized and fractionated in the interaction. Titanite is an important REE contributor to the regolith-hosted REE deposit. Here, we investigate textural and compositional variations of the titanite from the granitic bedrocks to weathered profiles in the Zuokeng regolith-hosted REE deposit, the largest one that is newly discovered in this region. Together with thermodynamic modelling, we deduce the nature of the fluids, temperature range for titanite alteration, and the mechanism of REE fractionation. Primary titanite is of magmatic in origin and shows relatively high REE contents and negative Eu anomaly on the chondrite-normalized REE pattern. Secondary titanite is commonly associated with chloritized biotite and is characterized by extremely low REE, high Al.sub.2O.sub.3, F and significant positive Eu anomaly, typical of authigenic origin due to chloritization of biotite under oxidized conditions in supergene environment. From the bedrocks upward to the surface, primary titanite is gradually replaced by calcite, synchysite-(Ce) and TiO.sub.2 in the weathered bedrocks. This is interpreted as the result of infiltration of the F, carbonate-rich, alkaline fluids derived from local groundwater through the bedrocks. The irregular dark patches in primary titanite display typical alteration texture and may have formed through fluid leaching of primary titanite. The patches in primary titanite have lower REE concentrations and higher LREE/HREE ratios than magmatic domains, indicating that the groundwater preferentially scavenges HREE from primary titanite, leaving behind LREE in weatherable secondary minerals, such as synchysite-(Ce) and allanite. Mass balance calculation results also confirm that more HREE are lost from weathered bedrocks than LREE. Therefore, the interaction of groundwater and granitic bedrocks may be favorable to enrich LREE rather than HREE in the regolith. This may explain why most regolith-hosted REE deposits like Zuokeng in South China are of predominant in LREE. This study highlights the role of groundwater in mobilizing, fractionating and enriching REE from the granitic bedrocks to resultant regolith-hosted REE deposits., Author(s): Jingzhao Dou [sup.1], Christina Yan Wang [sup.1] [sup.2] [sup.3], Yanlu Xing [sup.4], Wei Tan [sup.1] [sup.2] [sup.3], Zisong Zhao [sup.1] [sup.5] Author Affiliations: (1) grid.454798.3, 0000 0004 0644 5393, [...]