title: Minimising alkalinity and pH spikes from Portland cement-bound Bauxsol (seawater-neutralized red mud) pellets for pH circum-neutral waters.
abstract: 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 (H(2)0 + CO(2) or NaHCO(3)) or curing brines (CO(2), NaHCO(3), or Mg/CaCl(2)). 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 MgCl(2), CaCl(2) 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 245:1 (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.
authors.affiliation: School of Environmental Science and Management, Southern Cross University, PO Box 157, Lismore, NSW 2480, Australia. laure.despland@unine.ch
authors.forename: Laure M
authors.initials: LM
authors.lastname: Despland
authors.forename: Malcolm W
authors.initials: MW
authors.lastname: Clark
authors.forename: Michel
authors.initials: M
authors.lastname: Aragno
authors.forename: Tony
authors.initials: T
authors.lastname: Vancov
mesh_terms: D002119:Calcium Carbonate / Q000737:chemistry; D003252:Construction Materials / Q000032:analysis*; D052918:Environmental Restoration and Remediation; D006863:Hydrogen-Ion Concentration; D010710:Phosphates / Q000737:chemistry; D012623:Seawater / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry; D014865:Waste Disposal, Fluid / Q000379:methods*; D014867:Water / Q000737:chemistry
chemical_list: D010710:Phosphates; D014867:Water; D012822:Silicon Dioxide; D002119:Calcium Carbonate