Minimising Alkalinity and pH Spikes from Portland Cement-Bound Bauxsol (Seawater-Neutralized Red Mud) Pellets for pH Circum-Neutral Waters

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• 作者：Laure M. Despland ; Malcolm W. Clark ; Michel Aragno ; Tony Vancov
• 刊名：Environmental Science & Technology
• 出版年：2010
• 出版时间：March 15, 2010
• 年：2010
• 卷：44
• 期：6
• 页码：2119-2125
• 全文大小：198K
• 年卷期：v.44,no.6(March 15, 2010)
• ISSN：1520-5851

文摘

Bauxsol reagents (powder, slurry, or pellet forms) are powerful tools in environmental remediation and water and sewage treatment. However, when used in circum-neutral water treatments, cement-bound Bauxsol pellets produce a sustained pH and alkalinity spike due to the presence of unreacted CaO in the cement binder. This study developed a pellet treatment system to minimize the alkalinity/pH spike. The recipe for pelletization consisted of Bauxsol powder, ordinary Portland cement (OPC), hydrophilic fumed silica, aluminum powder, a viscosity modifier, and water. Several batches (including different ratios and sizes) were run using modified makeup waters (H₂O + CO₂ or NaHCO₃) or curing brines (CO₂, NaHCO₃, or Mg/CaCl₂). Alkalinity, pH stability, and slake durability tests were performed on pellets before and/or after curing. The best result for reducing the alkalinity/pH spike was obtained from a MgCl₂, CaCl₂ bath treatment using a Bauxsol:cement ratio of 2.8:1 (pH 8.28; alkalinity 75.1 mg/L) for a 100 g batch or 2.45:1 (pH 8.05; alkalinity 35.4 mg/L) for a 1 kg batch. Although brine curing does provide a control on pH/alkalinity release, the pellets may still contain unreacted CaO. Therefore, a freshwater rinse of pellets before treating circum-neutral waters is recommended as is the continued investigation of alternative pellet binders.