Tailored pH-triggered surfactant for stepwise separation of a three-component mineral system

Stepwise separation of multi-species with a single type of chemical additives (such as surfactants) is an auspicious but challenging issue in many engineering processes as one surfactant usually lacks the ability to interact with different components. One promising strategy is to develop an environment-responsive surfactant, which possesses various functional groups to anchor target constituents under different environmental conditions. In this work, we have prepared a pH-responsive surfactant (2-(benzylthio)-acetohydroxamic acid, BTHA) possessing two pH-switchable groups (i.e., thioether and hydroxamate) that can selectively interact with different target substances, thus enabling stepwise and efficient separation of a three-component mineral system. The single in-house synthesized BTHA is successfully applied to the sequential separation of pyrite, diaspore, and kaolinite from high-sulfur bauxite by simply tuning the solution pH. Specifically, under the acidic condition (pH 6.0), the hydroxamate group of BTHA is deactivated, thus only the thioether groups can directionally interact with pyrite and enable the selective flotation recovery of pyrite to 85.9%. When the solution pH is subsequently increased to 8.0, the active hydroxamate group of BTHA can tightly chelate with diaspore and result in its efficient separation from kaolinite. The bifunctional surfactant exhibits strong and selective interactions with target substrates via pH modulation, allowing the adsorption selectivity and efficient stepwise separation, which provides an innovative paradigm for the development of novel surfactants with diverse applications in the mineral, metallurgical, chemical, and renewables recycling industry.