Low Magnetite Research Articles

Understanding heavy mineral dynamics using magnetic fingerprinting technique: a case study of North Maharashtra Coast, India

Environmental magnetic and grain size measurements were carried out on sand samples collected from nine sand pits along a 20-km coastal stretch of Arnala Beach, North Maharashtra, India. This study sets out to identify the potential heavy (magnetite) mineral-rich sites in a dynamic coastal system and decipher their enrichment processes. Combination of rock-magnetic and grain size data of the sand pits mirrors the differential heavy mineral fluxes along the coast. Two distinct and well-separated bands of magnetite enrichments were identified. The upper magnetite band (UMB) is more pronounced and shows uniform magnetite enrichment representing the present-day beach erosional state. A well-separated lower magnetite band (LMB) had highest magnetite concentration at Vaitarna River mouth and depicts a strong decrease in magnetite content and clastic (mean) grain size away from the river mouth. This suggests that the NW–SE-directed coast-parallel sediment transport in the past played a major role in the formation of magnetite-rich layers of LMB. A non-enriched zone (NEZ) between UMB and LMB is magnetically weak and showed large variations in clastic grain sizes and possibly represents a period of sediment accretion. A strong correlation between magnetite concentration and magnetic grain size was found for all the sand pit samples, with highest magnetic susceptibility values being dominated by coarser magnetic grains. This relationship needs to be further exploited as a potential fingerprint to identify the heavy mineral lag deposits in coastal environments. Our study explores the potential of using environmental magnetism and sedimentological methods to identify the potential areas enriched in heavy (magnetic) minerals and explains the mechanism of their formation.

Ferric minerals and organic matter change arsenic speciation in copper mine tailings

Arsenic (As) is commonly associated with Cu ore minerals, with the resultant risk that As can be released offsite from mine tailings. We used synchrotron-based fluorescence X-ray absorption near-edge spectroscopy (XANES) imaging to provide in situ, laterally-resolved speciation of As within tailings which differed in magnetite content (5–12%) and organic matter content (0–5%). Although the total As content was lower in tailings with low magnetite (LM), the soluble (pore water) As was actually 7-times higher in LM tailings than in high magnetite (HM) tailings. Additionally, amendment with 5% sugarcane mulch residues (SMR) (for revegetation) further increased soluble As due to the dissolution and oxidation of arsenopyrite or orpiment. Indeed, in HM tailings, arsenopyrite and orpiment initially accounted for 88% of the total As, which decreased to 48% upon the addition of SMR – this being associated with an increase in AsV-ferrihydrite from 12% to 52%. In LM tailings, the pattern of As distribution and speciation was similar, with As as AsV-ferrihydrite increasing from 57% to 75% upon the addition of SMR. These findings indicate that changes in ore processing technology, such as the recovery of magnetite could have significant environmental consequences regarding the As mobilisation and transformation in mine tailings.

Magnetite recovery from copper tailings increases arsenic distribution in solution phase and uptake in native grass

Reprocessing magnetite-rich copper (Cu) tailings prompted a concern about arsenic (As) risks in seepage water and revegetated plants at Ernest Henry Cu Mine (EHM) in North Queensland, Australia, due to the closely coupled relationship between iron (Fe) minerals and As mobility. The magnetite removal alone significantly decreased the content of crystalline Fe minerals and the maximum arsenate (As(V)) sorption capacity of the resultant tailings. A glasshouse experiment with native grass Red Flinders (Iseilema Vaginiflorum) was conducted with the reprocessed (low magnetite (LM)) and original (high magnetite (HM)) tailings, which were amended with 5% sugarcane residue (SR) as a basal treatment in combination with 0, 1 and 5% pine-biochar (BC). The organic matter treatments and plant growth stimulated the formation of secondary Fe minerals. The amount of extractable amorphous Fe in the amended and revegetated HM tailings was significantly higher than those in the LM. Arsenic forms in the specifically sorbed and the sorbed by amorphous Fe oxides were significantly increased by the SR amendment in the LM tailings, but which were decreased in the HM, compared to the unamended tailings. Soluble As levels in the porewater of the LM under revegetation were significantly higher (300–1150 μg As L−1) than those (up to 45–90 μg As L−1) in HM tailings in the same treatment, which led to the higher As concentrations in the plants grown in the LM tailings. In particular, root As concentration (62–146 mg kg−1) in the LM tailings was almost a magnitude higher than those (8–17 mg kg−1) in the HM. The present results confirmed the initial expectation that the recovery of magnetite from the Cu tailings significantly elevated the risk of As solubility in the tailings by decreasing As sorption capacity and increasing soluble As levels. Thus, it would be beneficial to retain high contents of magnetite in the top layer (e.g., root zone) of the Cu tailings for managing As risk and revegetation in the future.

Magnetic characteristics of primary concentrates supplied as a feedstock to Abagur enrichment-agglomeration plant

The article presents basic magnetic characteristics of nine primary concentrates produced from Siberian magnetite ore and a lightly oxidized iron ore and supplied as a feedstock to Abagur enrichment-agglomeration plant. The best magnetic properties belong to the primary concentrate produced from the magnetite ore mined at Abaza, Irba and Kaz deposits; the weakest properties characterize the lightly oxidized ore from Izykh-Gol and Krasnokamensk; the magnetic characteristics are proportional to magnetite content in a primary test specimen. Considering this, the integrated processing of lightly oxidized and magnetite ore is recommended to lower magnetite loss in tailings of Abagur plant.

Microstructural characterization of surface layers formed on a low alloy steel during erosion – oxidation in a fluidized bed

Low alloy steel specimens were subjected to erosion-oxidation in a simulated fluidized bed environment in the range 100–600° C. Transmission electron microscopy was carried out on the surfaces which experienced particle impacts, with specimens prepared by backthinning. At low temperatures (≤ 200° C) a dense, protective layer of bed particle fragments formed on the steel surface due to fragmentation of particle asperities and their subsequent comminution to a very fine size (< 10 nm). At intermediate temperatures thin oxide films developed on the wear scar surfaces; these were predominantly magnetite with a fine grain size. There was rapid material loss with particle impacts removing the oxide and some metal below, but the thin oxide rapidly regrew due to the fine grain size, absence of a haematite layer and the mechanical damage during particle impact. At high temperatures the oxide became sufficiently thick to be mechanically protective. Erosion occurred within the fine grained surface haematite layer, while there was grain growth in the lower magnetite layer.