Calcium carbonate

Calcium carbonate precipitation and formation of clog particles inside the leachate
collection pipe can cause catastrophic failures in landfill operation. This study focuses on
quantifying the effectiveness of electronic scale control to reduce the clog formation within
the pipe network. A field scale model (40ft × 20ft) was constructed, featuring side-by-side
flow of electronically treated and untreated composite leachate. Data obtained in the first
phase of this study indicate that electronic scale control system does not have any
statistically significant effect on water quality parameters. The second phase of this study
identified calcite (CaCO3) to be the predominant phase present in the precipitates using
XRD/XRF diffraction pattern analyzed through a search match calculation program
(MATCH! Version 3.2.0) which concur with the previous studies. Furthermore, Rietveld
refinement using FullProf Suite confirms that there were no differences between the treated
and untreated precipitate based on the phases identified in the respective samples.

Different physiochemical processes control phosphorus storage in subtropical versus temperate estuaries; however, few studies are available on sediment phosphorus storage from the subtropics. In this study, solid-phase phosphorus pools of northeastern Florida Bay's sediments were examined by sequential chemical extractions, separating phosphorus into exchangeable, iron-bound, calcium-bound, and residual organic fractions. Calcium-bound phosphorus was the dominant fraction, accounting for approximately 60% of the total phosphorus and 93% of the inorganic phosphorus. Residual organic phosphorus was the second dominant fraction, accounting for 37% of the total phosphorus. In contrast to calcium-bound and residual organic phosphorus, the concentration of iron-bound phosphorus was low, indicating a limited role of iron in long-term phosphorus storage. The fine-grained carbonate sediments of Florida Bay probably account for the large pool of calcium-bound phosphorus, while the proximity of the mangroves to the northeastern section of the Bay may account for the high residual organic pool of phosphorus.

The effect of substrate finish and composition, flow rate and exposure duration on the composition, morphology and protective properties of calcareous deposits formed during cathodic polarization of several steels in seawater has been investigated. The current density behaviour of the scale formation in conjunction with morphology and composition characteristics indicated that the substrate finish and composition did not influence the nucleation or growth of the deposit. The results strongly suggest a relationship between electrolyte velocity, current density behaviour and morphology. With increased flow and consequent higher current density requirements, results indicated a low nucleation rate of CaCO3. The current density behaviour and composition of the calcareous deposit revealed a growth progression of a Mg rich film formed in the first few minutes, followed by an increasingly uniform surface coverage by CaCO3 in the form of aragonite.