Exploration of utilization of expired HCQS in oilfield water treatment: a case study of waste resource recycling

Since the emergence of COVID-19 in 2019, the accumulation of associated medications has led to the disposal of unused medicines, a process that currently consumes significant resources and contributes to carbon emissions. Oilfields, on the other hand, operate as a unique closed-loop system, where treated water is recycled internally without any external discharge. This unique setup offers an environment where disposed medicines will not interact with the biosphere. In this study, hydroxychloroquine sulfate (HCQS) tablets were employed as a fungicide and corrosion inhibitor in oilfield water treatment. Experimental results revealed that HCQS exhibits remarkable corrosion inhibition efficiency under acidic conditions. However, as the temperature rises, the corrosion inhibition efficiency diminishes. Specifically, at 333 K and a concentration of 200 mg/L, HCQS achieves a maximum corrosion inhibition efficiency of 90.86%. The adsorption behavior of HCQS on the surface of low-carbon steel follows the Langmuir adsorption isotherm, indicating a physical adsorption process. Thermodynamic simulations further indicate that the adsorption of HCQS onto the steel surface is an exothermic, spontaneous and entropy-reducing process. Electrochemical tests also demonstrated that HCQS acts as a mixed inhibitor, primarily suppressing the anodic reaction. Additionally, the antibacterial effects of HCQS were evaluated, revealing that at a concentration of 1000 mg/L, it effectively eliminates over 95% of three types of oilfield microorganisms. Finally, a cost-benefit analysis was conducted to assess the feasibility of applying this method, highlighting its simplicity, effectiveness and potential for resourceful disposal of waste medications.