Use of rice straw-based biochar for batch sorption of barium/strontium from saline water: Protection against scale formation in petroleum/desalination industries

The formation of hard mineral scale deposits (e.g., celestite (SrSO₄) and barite (BaSO₄)) is the most common problem that hinders sustainable operations of water-flooded oilfield and desalination systems (i.e., membrane fouling) when using poor quality water contaminated with barium (Ba(II)) and strontium (Sr(II)) ions. In this work, nanoscale biochar (∼53–712 nm) was synthesized from waste rice straw (cost = 380 to 560 ± 27 US$/Ton; n = 9) and applied as a protective approach against the formation of mineral scale deposits via adsorptive removal of Ba(II)/Sr(II) contaminants from 30,000 ppm saline wastewater. Adsorption of Ba(II)/Sr(II) ions onto biochar was investigated and optimized as a function of biochar amount, water pH, contact time, temperature, and Sr(II)/Ba(II) ratio using response surface methodology. Based on kinetic and isotherm analyses, the biochar exhibited enhanced potential to capture Sr(II)/Ba(II) ions via weak ion-exchange or pore-filling mechanisms (sorption energy (E)≈ 0.61–0.89 kJ/mol). A comparison of partition coefficient (PC) values verified that sorption of Sr(II) onto biochar is far superior to that of Ba(II) (PCs of 10.1 and 2.5 μmol g⁻¹ μM⁻¹, respectively). Sorption selectivity was mainly dependent on solution pH and the metallic properties of Ba(II)/Sr(II)(e.g., metal size, speciation, and mobility). Quantitative analysis of treated saline water using electrical conductivity and ion chromatography confirmed the ability of biochar sorbent to remove Ba(II) and Sr(II) ions (97.5%) with pre-desalination (e.g., salt reduction of 25.7% after 48 h). It is thus recommended to utilize the prepared biochar as a multifunctional alternative pre-desalinating ion-exchange medium to inhibit mineral scale formation via one-pot adsorption process before oilfield water flooding in the petroleum field and membrane desalination systems. Copyright © 2019 Published by Elsevier Ltd.