English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

Background  A proposed strategy for immobilizing trace metals in the subsurface is to stimulate calcium carbonate precipitation and incorporate contaminants by co-precipitation. Such an approach will require injecting chemical amendments into the subsurface to generate supersaturated conditions that promote mineral precipitation. However, the formation of reactant mixing zones will create gradients in both the saturation state and ion activity ratios (i.e.,a    CO    32  -/    a    C    a    2  +). To better understand the effect of ion activity ratios on CaCO 3  precipitation kinetics and Sr 2+  co-precipitation, experiments were conducted under constant composition conditions where the supersaturation state (Ω) for calcite was held constant at 9.4, but the ion activity ratio(   r  =    a    CO    32  -/    a    C    a    2  +)was varied between 0.0032 and 4.15.    Results  Calcite was the only phase observed, by XRD, at the end of the experiments. Precipitation rates increased from 41.3 ± 3.4 μmol m -2  min -1  at  r =  0.0315 to a maximum rate of 74.5 ± 4.8 μmol m -2  min -1  at  r =  0.306 followed by a decrease to 46.3 ± 9.6 μmol m -2  min -1  at  r  = 1.822. The trend was simulated using a simple mass transfer model for solute uptake at the calcite surface. However, precipitation rates at fixed saturation states also evolved with time. Precipitation rates accelerated for low  r  values but slowed for high  r  values. These trends may be related to changes in effective reactive surface area. Thea    CO    32  -/    a    C    a    2  +ratios did not affect the distribution coefficient for Sr in calcite (D P  Sr  2+ ), apart from the indirect effect associated with the established positive correlation between D P  Sr  2+  and calcite precipitation rate.    Conclusion  At a constant supersaturation state (Ω = 9.4), varying the ion activity ratio affects the calcite precipitation rate. This behavior is not predicted by affinity-based rate models. Furthermore, at the highest ion ratio tested, no precipitation was observed, while at the lowest ion ratio precipitation occurred immediately and valid rate measurements could not be made. The maximum measured precipitation rate was 2-fold greater than the minima, and occurred at a carbonate to calcium ion activity ratio of 0.306. These findings have implications for predicting the progress and cost of remediation operations involving enhanced calcite precipitation where mineral precipitation rates, and the spatial/temporal distribution of those rates, can have significant impacts on the mobility of contaminants.

The Effect of the CO32- to Ca2+ Ion activity ratio on calcite precipitation kinetics and Sr2+partitioning