A flow-injection system exploiting focused beam reflectance applied to the determination of high concentrations of sulfate

Abstract

To evaluate the grain size and particle number formed in a non-equilibrium flow mixing state, flow-injection analysis (FIA) was combined with focused beam reflectance measurement (FBRM). The influence of BaCl₂, PEG-4000, ethanol, flowrate, temperature and acidity on the dynamic formation of BaSO₄ particles was evaluated. Optimization parameters obtained were 5% BaCl₂ as the reagent, 2% PEG-4000 + 6% ethanol as the stabilizer and 0.3 mol L⁻¹ HCl as the carrier with 4 ml min⁻¹ flowrate, and the BaSO₄ particle size distribution in the system was in the 1–50 μm range. Under optimized conditions, the system was successfully used for the determination of high sulfate concentrations in the wet-process phosphoric acid process in the 3.2–48 g L⁻¹ (S_ct = 55c + 208, r = 0.998, n = 3) range for SO₄²⁻. The relative standard deviation was less than 1.86% (n = 11), the detection limit was 0.95 g L⁻¹, the sample throughput reached 30 samples per h, recovery data were within the 97–106% range, and the results were consistent with those of gravimetry (RD < 3%). The system avoids the large error caused by high dilution and the slow analysis speed when measuring high sulfate concentrations.