The influence of {Ba2+}:{SO42-} on particle charge, size and morphology during BaSO4 Crystal Nucleation and Growth in Aqueous Solutions

Abstract

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 (raq) at a fixed supersaturation (Ωbarite), 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 Ωbarite = 1000 with varying raq 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 raq < 1 during BaSO4 crystal formation and positive for raq > 1. At raq = 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 Ωbarite and raq.