No abstract

Hydrophobic associating polymers show great potential in formulation of high-performance drilling fluids, due to their hydrophobic associative ability in high-temperature and high-salt conditions. Herein, a novel amphoteric polyacrylamide of poly(acrylamide/2-acrylamido-2-methyl-1-propanesulfonic acid/methylacrylethyl trimethylammonium chloride) hydrophobically modified with epoxidized soybean oil denoted as PAADE was prepared and applied in water-based drilling fluid, and one without hydrophobic modification (PAAD) was also used for comparison. Compared with PAAD, PAADE displayed characteristic association behavior with a critical association concentration (CAC) of 0.3 w/v%, and a salt thickening phenomenon over 3 w/v% NaCl concentration. The impacts of PAADE and PAAD on rheological and filtration properties of bentonite-based drilling fluid (BTDF) were evaluated under different salinity. The fitted Herschel-Bulkley rheological parameters indicated that BTDF containing PAADE showed stronger yield stress, easier flowability and better salt resistance at a reasonable concentration below CAC. Meanwhile, PAADE largely reduced the fluid loss of BTDF before and after thermal aging at 150°C, showing high temperature tolerance. The addition of NaCl promoted larger reduction of filtration. The superior properties of PAADE in BTDF were revealed to be the competitive results of salt-induced hydrophobic association and inter-particles configuration transition. Moreover, the incorporation of epoxidized soybean oil improved the biodegradability of PAADE.

No abstract

Cadmium pollution in the soil induces significant hazards to agricultural growth and public health. Therefore, new routes are needed to develop low-cost soil amendments that can effectively stabilize cadmium and improve soil fertility. This study introduces modified illite (MIT) with the enhanced ability to stabilize heavy metal Cd through the mixing of illite with calcium carbonate, silicate and sulfate in specific proportions by using the well-known calcination-hydrothermal process. The characterization findings revealed that the modified MIT is predominantly composed of gehlenite and akermanite, with greatly improved specific surface area, pore structure and cation exchange capacity. The main purpose of the present study is to unravel a plausible mechanism on how MIT can stabilize Cd(II) in the soil and to investigate the effect of MIT on the fertility of the contaminated soil. Experiments on soil remediation revealed that MIT has a more profound stabilizing impact on Cd(II) compared to natural illite, resulting in a 22.84% reduction in acid-soluble Cd of the soil when MIT was dosed at 0.5%. The potential mechanism of Cd(II) immobilization by MIT involves the ionic exchange of Cd2+ with the exchangeable Ca2+ and Mg2+. In addition, the hydrolysis products of gehlenite and akermanite are prone to form silicate precipitates with free Cd, leading to soil pH increment. The pot experiments showed that MIT significantly reduces the cadmium content of soil and improves the growth of water spinach organs. Meanwhile, enhancement of the indicators in rhizosphere soil further proved that MIT effectively increases the nutrient content, improves the soil structure and promotes microorganism growth.