Integrated Process for CO2 Mineralization and Potassium Chloride Recovery from Cement Bypass Dust: A Pilot-Scale Study

Cement bypass dust (CBPD), a fine particulate by-product generated during cement manufacturing, contains large alkaline constituents such as calcium and potassium, present largely as soluble potassium chloride. In this study, a 1-ton-scale pilot plant was constructed to develop an integrated wet process that simultaneously achieves CO2 mineralization from CBPD and recovery of KCl. The process comprises two stages: (i) aqueous mineral carbonation of a CBPD slurry (solid-to-liquid ratio = 1:3) using cement kiln flue gas containing 14–18 vol% CO2, and (ii) KCl recovery via evaporative concentration and cooling crystallization. Three batches (TEST 1–3) were operated under varying conditions. The Ca conversion (η(Ca)), determined from complementary analyses of the filter cake (LOI, XRF and WPPF), ranged from 68.8 to 99.4%, while CO2 utilization (η(CO2)), defined as the ratio of fixed CO2 to supplied CO2, reached 62.8–84.3%. During leaching, 47.5–68.8% of potassium compounds in CBPD were transferred into the aqueous phase. Because KCl crystallizes with 1:1 stoichiometry, and potassium was the limiting component, this leaching efficiency set the upper bound of attainable KCl recovery. Across the three batches, 62.1 kg of dry crystalline KCl was recovered from 2204 kg of the feed CBPD. The purified KCl crystals exhibited purities of 92.3–99.03%; the first-pass product met the standard fertilizer grade (KCl ≥ 95%, K2O ≥ 60 wt%), whereas recycling of the mother liquor to increase overall recovery reduced the purity below this threshold due to Ca accumulation.