Two-Stage Methodology for the Quantitative Assessment of Fine-Dispersed Gold in Natural and Technogenic Objects

Fine-dispersed gold is difficult to quantify in natural and technogenic materials because it may occur as micron- and submicron-sized particles, films, inclusions, sorbed forms, and matrix-bound species. This study aims to provide a scientific basis for a two-stage methodology designed for the separate assessment of gravity-recoverable and hidden forms of gold. The proposed workflow includes gravity separation, ultrasonic aerohydraulic desliming, controlled thermal activation with a carbonaceous sorbent, low-temperature HCl-HNO3-HF acid digestion at 98 °C for 2 h, instrumental Au determination, statistical processing, and SEM-EDS verification. The studied materials included ores, weathering crusts, placer materials, gravity tailings, ash-slag waste, thermally treated products, and sorbents. Two analytical series, each consisting of 50 Au determinations, showed high heterogeneity, with Au contents ranging from 0.10 to 2.80 g/t and from 0.0259 to 5.0330 g/t, respectively. Gravity-separation balance data showed that a substantial proportion of Au may remain in the tailings. SEM-EDS revealed microheterogeneity, porous aggregates, microspheres, and candidate phases; however, it was used only for mineralogical verification rather than as a quantitative method for total Au determination. The proposed workflow improves the informativeness of hidden Au-form assessment and requires further laboratory standardization.