Application of sodium carbonate and sodium sulfate for removal of lithium and strontium from oilfield produced water

Produced water is the largest byproduct of oil and gas production, which contains various environmental contaminants such as heavy metals, salts, and organic compounds. Among all cations present in produced water, lithium and strontium are of particular environmental concern. Lithium poses potential toxicity to aquatic organisms, while strontium contributes to scale formation and facilitates the co-precipitation of naturally occurring radioactive materials. Although selecting an appropriate treatment method remains a significant challenge, chemical precipitation has demonstrated promising potential for cation removal. This study investigates the effectiveness of chemical precipitation for removing lithium and strontium from highly saline produced water obtained from an oil field in Iran. Sodium carbonate and sodium sulfate were applied at concentrations of 0.12, 0.14, and 0.16 M. Experiments were conducted at two temperatures, 25 °C and 90 °C, to assess the influence of temperature and salt concentration on precipitation efficiency. The results revealed that Na₂SO₄ was particularly effective in strontium removal, achieving a maximum removal efficiency of 86% at 90 °C and 0.16 M. In contrast, Na₂CO₃ exhibited limited efficacy in lithium removal, with a maximum removal rate of only 10%. The results imply that although both salts are promising choices to remove strontium, more optimization is needed to enhance lithium extraction, potentially employing multi-step treatments or other pretreatment techniques.