Closed-loop graphite intercalation technology

The industrial intercalation of graphite using aqueous oxidizing mixtures, followed by intercalate hydrolysis, results in the generation of significant volumes of wastewater. However, the composition of these effluents and viable methods for their treatment or reuse remain largely undocumented in the open literature. This study investigates the volume, chemical characteristics, and potential for cyclic reuse of wastewater generated during graphite intercalation processes. Graphite of grade GO-1, sourced from the Taiginskoye deposit, was used as the base material. The effectiveness of the intercalation process was assessed by the graphite expansion ratio at 500 °C. Sulfate ion concentrations were determined via titrimetric analysis according to GOST 31940–2012, and total chromium content was measured using the iodometric method per GOST 26473.10–85. It was established that production of 1 kg of intercalated graphite generates up to 200 liters of wastewater, classified by acidity into three categories: highly acidic (pH 0–1), moderately acidic (pH 2–4), and weakly acidic to near-neutral (pH 5–6). Sulfate concentrations ranged from 12.10 to 3.80 g/L, and total chromium content from 2.49 to 0.30 g/L—substantially exceeding regulatory limits. Experimental results confirm the feasibility of cyclically reusing highly acidic wastewater (pH 0–1) in the oxidizing mixture. This approach allows for a 1.7-fold reduction in sulfuric acid and potassium dichromate consumption, without compromising the degree of graphite expansion, which remained stable in the range of 39–43 at 500 °C.