Accelerated mineral bio-carbonation of coarse residue kimberlite material by inoculation with photosynthetic microbial mats.

Microbiological weathering of coarse residue deposit (CRD) kimberlite produced by the Venetia Diamond Mine, Limpopo, South Africa enhanced mineral carbonation relative to untreated material. Cultures of photosynthetically enriched biofilm produced maximal carbonation conditions when mixed with kimberlite and incubated under near surface conditions. Interestingly, mineral carbonation also occurred in the dark, under water-saturated conditions. The examination of mineralized biofilms in ca. 150 µm-thick-sections using light microscopy, X-ray fluorescence microscopy (XFM) and backscatter electron-scanning electron microscopy-energy dispersive x-ray spectrometry demonstrated that microbiological weathering aided in producing secondary calcium/magnesium carbonates on silicate grain boundaries. Calcium/magnesium sulphate(s) precipitated under vadose conditions demonstrating that evaporites formed upon drying. In this system, mineral carbonation was only observed in regions possessing bacteria, preserved within carbonate as cemented microcolonies. 16S rDNA molecular diversity of bacteria in kimberlite and in natural biofilms growing on kimberlite were dominated by Proteobacteria that are active in nitrogen, phosphorus and sulphur cycling. Cyanobacteria based enrichment cultures provided with nitrogen & phosphorus (nutrients) to enhance growth, possessed increased diversity of bacteria, with Proteobacteria re-establishing themselves as the dominant bacterial lineage when incubated under dark, vadose conditions consistent with natural kimberlite. Overall, 16S rDNA analyses revealed that weathered kimberlite hosts a diverse microbiome consistent with soils, metal cycling and hydrocarbon degradation. Enhanced weathering and carbonate-cemented microcolonies demonstrate that microorganisms are key to mineral carbonation of kimberlite.

Accelerated carbonate biomineralisation of Venetia diamond mine coarse residue deposit (CRD) material - A field trial study.

Field trials combining mined kimberlite material (Coarse Residue Deposit; CRD) and mine derived microbes show accelerated kimberlite weathering at surface conditions - a potential method for accelerated carbon sequestration via mineral bio­carbonation. A photosynthetic biofilm suspension (20L), sourced from the Venetia diamond mine (Limpopo, South Africa) pit wall, was cultured in 3 × 1000 L bioreactors using BG-11 medium. Bioreactors supplemented with Fine Residue Deposit (FRD) kimberlite material enhanced microbial growth and kimberlite weathering. This (ca. 1.44 kg) wet weight bio-amendment corresponded to ca. 1.5 × 109Acidithiobacillus spp. sized bacteria/g CRD (20 kg FRD growth supplement +60 kg FRD used for harvesting biomass +850 kg CRD used in the field trial experiment). This bio-amendment promoted carbonate precipitation and subsequent cementation under surface conditions (0-20 cm). Microbial inoculation accelerated pedogenesis of CRD materials. A soil-like substrate resulted from weathering under environmental conditions in Johannesburg from January 2020 to April 2021. Over this 15-month experiment, the biodiversity found in the inoculum shifted due to the selective pressure of the kimberlite. The natural, endogenous biosphere, when combined with the inoculum, accelerated carbonate precipitation in the upper 20 cm of the bioreactor by between +1 wt% and + 2 wt%. Conversely, carbonation of the bioreactor at depth (20-40 cm) decreased by ca. 1 wt%. All the secondary carbonate observed in the bioreactors was biogenic in nature, i.e., possessing microbial fossils. This secondary carbonate took the form of both radiating acicular crystals as well as colloform intergranular cements. This microbial inoculum and resulting geochemical changes promoted the transformation of kimberlite into a Technosol, capable of supporting the germination and growth of self-seeding, windblown grasses, which enhanced weathering in the rhizosphere. The maximum secondary carbonate production is consistent with a ca. 20 % mine site CO2e offset.

Biochemical synthesis of palladium nanoparticles: The influence of chemical fixatives used in electron microscopy on nanoparticle formation and catalytic performance.

Palladium nanoparticles (PdNPs) can catalyse a range of reductive chemical reactions transforming both organic and inorganic environmental pollutants. PdNPs that ranged from <2 to 2-40 nm were synthesized using chemical methods, and bacterial biomass with/without chemical fixatives. PdNP formation was enhanced by adsorption of Pd(II) to bacterial biomass, followed by fixation with formate or glutaraldehyde. TEM-SAED analyses confirmed that the cell associated PdNPs were polycrystalline with a face-centered cubic structure. Chemically formed PdNPs possessed a higher Pd(0):Pd(II) ratio and produced structurally similar nanoparticles as the biotic systems. These PdNPs were employed to catalyze two, reductive chemical reactions, transforming 4-nitrophenol (4-NP) and hexavalent chromium [Cr(VI)], into 4-aminophenol and Cr(IV), respectively. In the reduction of 4-NP, the catalytic performance was directly proportional to PdNP surface area, i.e., the smallest PdNPs in formate-PdCH34 cells had the fastest rate of reaction. The mass of Pd(0) as PdNPs was the main contributor to Cr(VI) reduction; the chemically synthesized PdNPs showed the highest removal efficiency with 96% at 20 min. The use of glutaraldehyde enhanced the reduction of Pd(II) and promoted PdNPs formation, i.e., creating an artefact of fixation; however, this treatment also enhanced the catalytic performance of these PdNPs.