Determination of Ti, Zr, Al, Fe, Mg, Si and P in Offshore Placer Deposits by Inductively Coupled Plasma-Optical Emission Spectrometry with Sodium Hydroxide Fusion

Offshore sand deposits contain abundant heavy mineral resources, such as zircon (ZrSiO₄), ilmenite (FeTiO₃), rutile (TiO₂), anatase (TiO₂), monazite (Ce,La,Nd,Th)PO₄, garnet and so on, and therefore exhibit substantial development potential This study establishes a method that integrates NaOH alkali fusion, oscillator-assisted crucible release via HCl redissolution, and inductively coupled plasma optical emission spectrometry, in order to simultaneously determine the contents of titanium, zirconium, aluminum, iron, manganese, silicon, and phosphorus in marine placer deposits. A 1.0g of low-melting NaOH is used as flux to fuse the sample at 650˚C for 30 min. After cooling, the crucible together with the melt are transferred into a 20% HCl solution, and dissolution is completed by shaking in a constant temperature oscillator. Systematic optimization of flux mass, fusion duration, and oscillator-assisted crucible release time eliminates the high-temperature bumping, crucible corrosion, incomplete crucible-releasing, and cumbersome sample pretreatment. The procedure is streamlined yet analytically robust. Careful manipulation of the HCl concentration, not only neutralizes the residual alkaline flux, but also suppresses aggressive acid attack on the nickel crucible, substantially prolonging its service lifetime. Coupled with controlled mechanical agitation, the protocol ensures homogeneous dispersion and rapid solubilization of the molten residue, facilitating quantitative liberation of the target analytes into the solution phase. Under optimal conditions, the detection limits of this method for SiO₂, Al₂O₃, and Fe₂O₃ (total iron) in offshore placer deposits are between 0.01% and 0.06%, while the detection limits for Mn, P, Ti, and Zr range from 2.67µg/g to 14.30µg/g, with a precision not exceeding 4.67%. After verification with various primary national standard reference materials, the relative error of each element is ≤4.57%, meeting the requirements of “The Specification of Testing Quality Management for Geological Laboratories”.