In this study, Bauxsol pellets packed in PVC columns were used to remove nutrients and trace-metals from municipal wastewater during a 6 months field trial. Bauxsol pellet columns showed a high phosphate removal rate via precipitation of PO(4)(3-) with Ca(2+) and Mg(2+) ions: at 90% in the 1st month; at 80% from the second to fifth months; and at 60% in the sixth month. Pellet bound total phosphorus and Colwell phosphorus were 7.3 g/kg and 2 g/kg and are about 20 times the concentrations found in most fertile soils. Trace-metals in effluents were bound, probably irreversibly under the columns' environmental conditions, to the Bauxsol minerals that have high surface area to volume ratios and high charge to mass ratios. Experimental results showed a complex nitrogen cycle operating within the Bauxsol pellet columns including anoxic nitrification, denitrification, and anammox processes. Although a transient pH spike, associated with the release of unreacted CaO from the cement binder used in the pellets, was observed, this may be readily corrected through post-treatment pH adjustment. Hence, the geochemistry of Bauxsol pellets can effectively remove and bind nutrients and trace-metals during wastewater treatment, and further research may show that saturated spent pellets can be used as fertilizer.

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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.

Sugarcane bagasse ash re-utilisation has been advocated as a silica-rich feed for zeolites, pozzolans in cements and concretes, and geopolymers. However, many papers report variable success with the incorporation of such materials in these products as the ash can be inconsistent in nature. Therefore, understanding what variables affect the ash quality in real mills and understanding the processes to characterise ashes is critical in predicting successful ash waste utilisation. This paper investigated sugarcane bagasse ash from three sugar mills (Northern NSW, Australia) where two are used for the co-generation of electricity. Data shows that the burn temperatures of the bagasse in the high-efficiency co-generation boilers are much higher than those reported at the temperature measuring points. Silica polymorph transitions indicate the high burn temperatures of ≈1550 °C, produces ash dominated α −quartz rather than expected α-cristobilite and amorphous silica; although α-cristobilite, and amorphous silica are present. Furthermore, burn temperatures must be ≤1700 °C, because of the absence of lechatelierite where silica fusing and globulisation dominates. Consequently, silica-mineralogy changes deactivate the bagasse ash by reducing silica solubility, thus making bagasse ash utilisation in synthetic zeolites, geopolymers, or a pozzolanic material in mortars and concretes more difficult. For the ashes investigated, use as a filler material in cements and concrete has the greatest potential. Reported mill boiler temperatures discrepancies and the physical characteristics of the ash, highlight the importance of accurate temperature monitoring at the combustion seat if bagasse ash quality is to be prioritised to ensure a usable final ash product.