The influence of {Ba²⁺}:{SO₄^2-} on particle charge, size and morphology during BaSO₄ Crystal Nucleation and Growth in Aqueous Solutions

Barite (BaSO₄) is a major nuisance in terms of scale in oil and gas recovery and in the use of geothermal energy. Therefore, it is essential to study the physico-chemical paramaters influencing the particle charge, size, morphology and timing of formation, providing new insight into mitigating BaSO₄ scale formation. In this study, the impact of solution stoichiometry (r_aq) at a fixed supersaturation (Ω_barite), upon the formation (i.e. nucleation + growth) of BaSO₄ crystals in 0.02 M NaCl suspensions, on the development of particle size, charge and morphology was investigated using Dynamic Light Scattering (DLS), Mixed-Mode Measurement – Phase Analysis Light Scattering (M3-PALS) and Scanning Electron Microscopy (SEM). DLS batch experiments showed that the average particle size in all suspensions at Ω_barite = 1000 with varying r_aq of the largest population present grew from ~ 200 to ~ 700 nm within 10 to 15 minutes and grew fastest near the ideal 1:1 stoichiometric ratio and more slowly at non-stoichiometric conditions. Additional flow DLS measurements at the same initial conditions confirmed that BaSO₄ nucleation kinetics were very fast and showed strong signs of aggregation of prenucleation clusters, which formed particles in the range of 200 – 300 nm. M3-PALS batch experiments  showed that the charge stayed negative for r_aq < 1 during BaSO₄ crystal formation and positive for r_aq > 1. At r_aq = 1, positive and negative populations of particles prevailed for 2.5 hours before circumneutrally charged particles remained. Moreover, SEM results showed that morphology is drastically affected by Ω_barite and r_aq.