Efficient microwave-assisted digestion of geological materials with HBF4: a reduced-hazard alternative to HF

Microwave-assisted digestion using tetrafluoroboric acid (HBF4) was evaluated as a reduced-hazard alternative to hydrofluoric acid (HF) for elemental analysis of geological materials. Six geological reference materials spanning a range of lithologies and compositions relevant to sedimentary paleoenvironmental investigations (BHVO-2, SCo-2, SSAR-1, MESS-4, NOD-A-1, and ShBOQ-1) were digested using an automated microwave system and analysed for elemental concentrations by ICP-MS/MS. Near-quantitative recovery of refractory silicate- and oxide-associated elements, including Cr, Co, and Ni, indicates effective dissolution of resistant mineral phases, although minor under-recovery of Ti and Zr suggests that digestion may not have been fully quantitative for all refractory minerals. In contrast, Mg, Al, Ca, rare earth elements (REEs), and Th exhibited notably reduced recoveries, inferred to result from the precipitation of insoluble fluorides and oxides—a limitation common to fluoride-based digestion methods. Despite this, the method enables efficient microwave-assisted sample processing and is well suited for the determination of REE profiles and concentrations of light transition metals (V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As) and many trace elements (Be, Na, P, S, K, Nb, Sb, Ba, Tl, Pb, U) from geological materials, while presenting lower hazards relative to conventional HF-based digestion procedures.