Jonathan Richard Lloyd

The Saudi Arabian mining sector is expanding rapidly. Among the strategic resources under investigation are bauxite ore and its industrial byproduct, red mud, both of which have potential as secondary sources of REEs. This study characterizes the mineralogical and geochemical properties of bauxite and red mud to evaluate REE distribution and behavior. Two groups of bauxite in the Al Ba’itha mine have been petrologically identified: (i) a high-Al group and (ii) a high-Fe ferruginous group. The bauxite was predominantly composed of gibbsite and boehmite, followed by kaolinite, with lesser amounts of hematite, anatase, minor goethite, quartz and calcite. In contrast, red mud generated via the Bayer process predominantly contained hematite and goethite, along with sodalite and cancrinite, and minor residual gibbsite and boehmite, as well as calcite, rutile, anatase, and quartz. The analyzed bauxite averages ~60 wt.% Al₂O₃, primarily from gibbsite and boehmite, affirming its value as an aluminum ore. The red mud was ~27 wt.% Fe₂O₃ and ~22 wt.% Al₂O₃, reflecting its mineralogical complexity and enrichment in iron and aluminosilicate phases. ICP-MS analysis revealed notable REE concentrations: bauxite contained Ce (142.5 ppm), La (63.2 ppm), and Nd (40.0 ppm), while the red mud exhibited higher concentrations of Ce (256 ppm), La (112 ppm), and Nd (77.2 ppm), with total REE contents exceeding 500 ppm. REEs were primarily associated with Al-bearing phases in bauxite, while Dy and Eu could also be associated with Fe-bearing phases. In contrast, HREEs showed a strong positive correlation with Fe₂O₃ in red mud. These findings highlight Saudi red mud as a strategic secondary REE resource within the rapidly expanding Saudi mining sector. They demonstrate strong economic potential and align with global trends seeking sustainable, residue-based pathways for REE recovery.

Microbial recovery of Pd, Pt, and Rh enables the green biosynthesis of bimetallic PdPt and PdRh nanoparticles, including novel PdRh alloys, which show high catalytic activity for 4-nitrophenol reduction.

In a geological disposal facility for radioactive waste, groundwater interacts with engineered cement barriers used for waste encapsulation, as a backfill material, and for construction purposes. This study investigates microbial interactions with low-pH cement (pH 10.5 and 11) in synthetic groundwater under anoxic conditions. Microcosm experiments used alkaliphilic microbes obtained from a high-pH lime kiln site. These were incubated with low-pH cement tablets in synthetic Oxford clay porewater with varying levels of electron donors (lactate or hydrogen) or electron acceptors (nitrate). In higher-carbon systems supplemented with lactate, reduction of nitrate was noted over six months, decreasing pH (10.0 to 8.8), presumably due to carbonic acid production. Calcium concentrations also dropped (9.2 to 4.7 mM). SEM-EDS and μ-XCT analyses confirmed that calcium carbonate precipitates had healed cracks and reduced porosity in the cement tablets. However, in the low-carbon system, microbial activity was minimal, leading to smaller pH changes (from 10.0 to 9.4) and greater leaching of Ca²⁺ and Mg²⁺ from the cement. This indicates that less carbonate was produced, and the reduction in pore size over six months was smaller compared to the high-carbon system. 16S rRNA gene sequencing revealed an increased abundance of alkaliphilic nitrate-reducing bacteria, including Anaerobacillus species, which were enriched in high-carbon treatments. Overall, findings suggest that in low-carbon environments, cement will gradually leach cations. By contrast, elevated organic carbon levels (e.g., from cementitious waste) can stimulate microbial activity, enhancing calcite precipitation, crack healing, and pore-clogging, which could improve cement barrier performance and limit contaminant migration.

Shewanella oneidensis MR‐1 can biosynthesize cell‐supported Cu‐nanoparticles (CuNPs), via the bioreduction of Cu(II) _(aq) , with excellent catalytic activity for click chemistry reactions. However, enzymatic mechanisms underpinning Cu(II) bioreduction were unclear. Here, the oxidation of hydrogen as electron donor was essential for Cu(II) bioreduction by S. oneidensis and hydrogenase deletion mutants were used to demonstrate the critical role of the periplasmic [NiFe] hydrogenase, HyaB. Wild type (WT) cultured cells coupled hydrogen oxidation to biosynthesis of Cu(0)/Cu(I)‐NPs within the periplasm (identified using XRD and TEM with SAED, EDS, EELS); ΔhyaB mutants did not produce CuNPs. Biosynthesized CuNPs were catalytically active for the cycloaddition of methyl azidoacetate and 1‐hexyne, confirming the potential for microbial revalorization of Cu(II)‐containing wastewaters, by forming catalytically active nanomaterials. Identifying HyaB, as a key mediator for Cu(II) reduction in S. oneidensis is an important first step towards developing industrial bioprocesses for Cu(II) recovery and CuNP synthesis, offering a template for improvements using engineering biology. Interestingly, c ‐type cytochromes, critical for reduction of other metals, were unable to fully reduce Cu(II) _(aq) in vivo despite being capable of Cu(II) reduction under in vitro conditions. In fact, Cu inhibited outer membrane cytochrome mediated reduction of Pd(II), and this may impact bioreduction of mixed metal solutions/effluents.

Hydraulic fracturing generates large volumes of flowback and produced water, composed of complex mixtures of organic and inorganic constituents. The solids associated with these fluids are Fe-rich and can contain toxic organics, heavy metals and naturally occurring radioactive materials (NORMs). Despite this, only a few studies have analysed their composition and there is a lack of understanding about their interactions with microbial communities and their long-term fate in the environment. In this study, we analysed the solids associated with flowback water derived from a hydraulically fractured well in the Bowland Shale, UK. We also investigated the microbial reduction of these Fe(III)-rich materials under anaerobic conditions using anthraquinone-2.6-disulfonate (AQDS) as an electron shuttle and identified the resulting bioreduced mineral phases. XRD characterization indicated that the solids contained akaganeite (β-FeOOH, Cl) and Ba-bearing celestine (SrSO₄). These Fe(III)-containing solids served as an electron acceptor for Shewanella frigidimarina and a flowback-derived Fe(III)-reducing enrichment culture. The bioreduced Fe(II)-bearing mineral phase was identified as ankerite [Ca(Fe,Mg,Mn)(CO₃)₂]; however, the presence of amorphous mineral phases is not ruled out. Microbial community composition was analysed using 16S rRNA gene sequencing. Amplicon sequence variants (ASVs) most closely related to Chromohalobacter, Caminicella and putative Fe(III)-reducing genera were dominant across treatments. Our findings highlight the potential of these Fe(III)-bearing sludges to be harnessed for the development of wastewater treatment strategies; for example, coupling the oxidation of toxic organics with Fe(III) reduction through either the introduction of microbial inocula or biostimulation of the native microbial communities. Furthermore, microbial processing can also be optimized to transform the Fe(III) sludges into denser materials, which are easier to handle and can immobilize toxic metals, thereby reducing the toxicity of this waste.

Removal of U( vi ) in oxic groundwaters through the formation of low solubility U( vi ) phosphate (bio)minerals, expanding the treatment envelope for in situ biomineralisation technologies.

Background: Biogeochemical processing of metals including the fabrication of novel nanomaterials from metal contaminated waste streams by microbial cells is an area of intense interest in the environmental sciences. Results: Here we focus on the fate of Ce during the microbial reduction of a suite of Ce-bearing ferrihydrites with between 0.2 and 4.2 mol% Ce. Cerium K-edge X-ray absorption near edge structure (XANES) analyses showed that trivalent and tetravalent cerium co-existed, with a higher proportion of tetravalent cerium observed with increasing Ce-bearing of the ferrihydrite. The subsurface metal-reducing bacterium Geobacter sulfurreducens was used to bioreduce Ce-bearing ferrihydrite, and with 0.2 mol% and 0.5 mol% Ce, an Fe(II)-bearing mineral, magnetite (Fe(II)(III)₂O₄), formed alongside a small amount of goethite (FeOOH). At higher Ce-doping (1.4 mol% and 4.2 mol%) Fe(III) bioreduction was inhibited and goethite dominated the final products. During microbial Fe(III) reduction Ce was not released to solution, suggesting Ce remained associated with the Fe minerals during redox cycling, even at high Ce loadings. In addition, Fe L_2,3 X-ray magnetic circular dichroism (XMCD) analyses suggested that Ce partially incorporated into the Fe(III) crystallographic sites in the magnetite. The use of Ce-bearing biomagnetite prepared in this study was tested for hydrogen fuel cell catalyst applications. Platinum/carbon black electrodes were fabricated, containing 10% biomagnetite with 0.2 mol% Ce in the catalyst. The addition of bioreduced Ce-magnetite improved the electrode durability when compared to a normal Pt/CB catalyst. Conclusion: Different concentrations of Ce can inhibit the bioreduction of Fe(III) minerals, resulting in the formation of different bioreduction products. Bioprocessing of Fe-minerals to form Ce-containing magnetite (potentially from waste sources) offers a sustainable route to the production of fuel cell catalysts with improved performance. Graphical

The biosynthesis of Pd nanoparticles supported on microorganisms (bio‐Pd) is achieved via the enzymatic reduction of Pd(II) to Pd(0) under ambient conditions using inexpensive buffers and electron donors, like organic acids or hydrogen. Sustainable bio‐Pd catalysts are effective for C‐C coupling and hydrogenation reactions, but their industrial application is limited by challenges in controlling nanoparticle properties. Here, using the metal‐reducing bacterium Geobacter sulfurreducens, it is demonstrated that synthesizing bio‐Pd under different Pd loadings and utilizing different electron donors (acetate, formate, hydrogen, no e⁻ donor) influences key properties such as nanoparticle size, Pd(II):Pd(0) ratio, and cellular location. Controlling nanoparticle size and location controls the activity of bio‐Pd for the reduction of 4‐nitrophenol, whereas high Pd loading on cells synthesizes bio‐Pd with high activity, comparable to commercial Pd/C, for Suzuki–Miyaura coupling reactions. Additionally, the study demonstrates the novel synthesis of microbially‐supported ≈2 nm PdO nanoparticles due to the hydrolysis of biosorbed Pd(II) in bicarbonate buffer. Bio‐PdO nanoparticles show superior activity in 4‐nitrophenol reduction compared to commercial Pd/C catalysts. Overall, controlling biosynthesis parameters, such as electron donor, metal loading, and solution chemistry, enables tailoring of bio‐Pd physicochemical and catalytic properties.