<p> A simplistic equilibrium, computer model was devised to simulate the removal of orthophosphates from wastewater. The components of the model were calcium, magnesium, carbonate and orthophosphate present as simple hydrated ions, ligands, acid-base dissociation products, ion pairs, ion pair complexes, ion complexes and precipitates. Data from laboratory experiments were tested in the model to determine the apparent activity products of calcite, hydroxyapatite, tricalcium phosphate and brucite. The results indicated a degree of supersaturation of hydroxyapatite between 15 to 20 orders of magnitude dependent on the aqueous species included in the calculations. The apparent pKsp values for different sets of data showed the mean ranging from 95 to 102.5 with standard deviations 2 to 5. The inclusion of the aqueous ion complexes Ca2·HPO4·CO^o 3 and Ca2·PO4·CO- 3 when calculating the apparent activity products results in a pKsp of 102.5 which varies little with pH or the presence of magnesium. The solubility of tricalcium phosphate varies more with pH than hydroxyapatite, a mean pKsp of 26.8 was calculated which compares favourably with the pKsp of 27.0 quoted in the literature. The apparent activity product of brucite was strongly dependent on pH while that of calcite was extremely variable. When hydroxyapatite precipitated, there was a minimum residual phosphate between pH 8.5 - 9.0, followed by an increase of phosphates in solution due to calcium being removed by the precipitation of calcite. Beyond pH 10, the phosphate concentration in solution decreased rapidly as there was an increase in the precipitation of hydroxyapatite coupled with a decrease of calcite. Under identical initial conditions, the precipitation of tricalcium phosphate compared to hydroxyapatite resulted in similar orthophosphate residuals. The use of the apparent activity products compared to literature solubility products results in 2 to 3 orders of magnitude greater phosphate residuals in solution.</p> / Thesis / Master of Science (MSc)

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Calcite stalactites ranging in length from several inches to a foot long are found forming on the southeastern slag pile at the former Gadsden Steel Mill of the Gulf States Steel Corporation. Analyses of samples collected per EISOPQAM guidelines include the following: petrographic, conductivity, pH, XRD, XRF, TDS, and major cations and anions. Preliminary field pH and conductivity measurements indicate that waters near the slag pile have a pH ranging from 11-12 and a conductivity ranging from 1115-6300 μS/ cm. Titration data indicate that the maximum pH value is 12.5. These calcite stalactites and stream coatings result from the dissolution of the steelmaking slag by rainfall. These alkaline waters precipitate calcite when they are in contact with atmospheric CO2. Improper management of slag products can lead to aesthetically impacted environments and ecosystems. Several studies and this study show that steel slag could be used to sequester atmospheric CO2.

Microbial Induced Calcite Precipitation (MICP) is an attractive alternative for a variety geotechnical ground improvement practices commonly used today and has a variety of potential applications. This research focuses primarily on its use as a soil stabilization technique using the bacteria Sporosarcina Pasteurii and a single injection point percolation method adapted from previous research in granular soils. This method, and most published data, show an inherent variability in both physical and engineering properties due to the distribution of precipitated calcite within the specimen. The focus of this research is on the quantification of the variability in shear strength parameters induced by MICP treatment in sand. Also, on the initial development of a new treatment method which aims to reduce this inherent variability and offer a more feasible option for field applications. The MICP treated soil columns were sampled at constant intervals from the injection point and then subject to direct shear testing (DST) and calcite distribution analysis. This analysis reiterates previously documented reduction in cementation as distance from injection point increases. The reduction in cementation results in reduced shear strength parameter improvements. This research also concluded a minimum of two percent mass of calcite per total mass of treated soil for significant strength improvements.

Microbially induced calcite precipitation (MICP) has been used for a number of years as a technique for the improvement of various geological materials. MICP has been used in a limited capacity in organic rich soils with varying degrees of success. Investigators hypothesized that microbially-induced cementation could be improved in organic soils by using a surfactant. Varying amounts of Sodium Dodecyl Sulfate (SDS) were added to soils of varying organic content and a mixing procedure was used to treat these soils via MICP. Treated specimens were tested for unconfined compressive strength (UCS). Results appeared to show direct relationships between SDS content and treated specimen strength although significant variability was present in the data. In addition, results also indicated that while addition of SDS during MICP treatment strengthens soil, the strengthening is likely from the formation of a calcium dodecyl sulfate (CDS) complex in which the CDS surrounds the soil in a matrix, and formation of MICP-induced calcite has very little to do with overall soil performance. As such, a new method for stabilizing loose soils dubbed ‘Surfactant-induced soil stabilization’ (SISS) was further explored by treating additional soil specimens. Samples treated using this technique showed increases in strength when compared to untreated specimens. In addition, preliminary data indicated that SISS treated specimens were insoluble. The SISS technique presents a number of advantages when compared to traditional soil stabilization techniques. In particular it should be relatively low-cost and simple to administer since its only components are SDS and calcium chloride. Additionally, these constituents are relatively more sustainable than chemicals associated with more-traditional loose soil stabilization techniques.

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