The precipitation of calcium carbonate is well studied in many fields of research and industry. Despite the fact that, or perhaps because of the fact that, it is well studied in many fields, different approaches have been used to describe the kinetics of the precipitation process. The aim of this study was to collect and compare the data available in the literature and find a consistent method to describe the kinetics of growth and nucleation of the various polymorphs of calcium carbonate. Inventory of the available data showed that a significant number of the literature sources were incomplete in providing the required information to recalculate the kinetic constants. Using a unified method, we obtained a unique set of parameters to describe the kinetics for growth for calcite, vaterite and amorphous calcium carbonate (ACC) and nucleation for vaterite and ACC. Recalculation of the kinetic constants demonstrated that calcite confirmed there are two growth mechanisms within one polymorph, namely pure spiral growth and spiral growth mixed with surface nucleation. The spiral growth does not show second-order growth, which is typically attributed to it. Re-evaluation of the available nucleation data confirmed the suggested existence of a second pure ACC polymorph with a solubility product between 10−5.87 and 10−5.51 mol2 kgw−2 .@en

One of the major challenges of in situ applied ground improvement techniques like Microbial and Chemical Induced Calcite Precipitation (MICP and CICP) is the homogeneous or at least spatially controlled, distribution of the desired reaction products in order to obtain controlled improvement of geotechnical bulk soil properties (Redding, 2007; Van Paassen, 2009 Numerical modelling simulations at continuum (Darcy) scale are performed to study the spatial distribution of reaction product(s) as a function of the injection strategy. An example of the simulations is shown in the figure below. The models are validated with laboratory experiments using a quasi two dimensional flow box with a large number of ports which could be either used as injection/extraction well or as a sensor port. This article presents the results obtained when multiple injection wells are operated simultaneously in which two reactive solutions (calcium chloride and sodium (bi-) carbonate) are injected separately in alternating wells located perpendicular to the background flow. Water is used as a non-reactive spacer. Hydraulic pressures and electrical resistivity tomography (ERT) are used in the laboratory set-up to monitor the spatial distribution of reactants and products. The shape and location of the mixing zone during treatment, and the spatial distribution of calcium carbonate after treatement are evaluated for different injection strategies. @en

Microbially induced precipitation is a multi disciplinary field combining biology, chemistry and geotechnology. An example of such a process is biogrout, where high concentrations of calcium ions together with biological carbonate production is used to precipitate calcium carbonate in soils. To be able to describe the precipitation rate, the chemical saturation, which is needed for the driving force of precipitation, must be calculated properly. A small deviation in the saturation can lead to large deviations n crystal growth and nucleation rates Calculating the saturation in a carbonate system requires ion speciation and activity corrections to be taken into account. There are many activity correction methods available, most of which are only valid up to a moderate ionic strength of the solution ( < 0.1 mol kg^-1) Some of these methods are also developed for equimolar electrolytes. This is in contrast with the biogrout process which involves solutions with high ionic strengths and calcium and carbonate concentrations which are initially strongly non-equimolar Additionally, the calculation of saturation can be simplified by ignoring several ion complexes and water self-ionization. However, simplifications must be made with care as the speciation is strongly non linear. This means that any simplification may have a significant impact on the saturation This research aimed to compare several softwares using different activity correction methods, e.g PhreeqC, as well as a full speciation scheme coupled with an activity correction method suitable for solutions with a high ionic strength Their performance for solutions with ionic strength and non-equimolar concentrations are tested Additionally, this research aims to provide a speciation scheme for such solutions that is simplified as much as possible without significant accuracy loss for the chemical saturation@en

A case study and computer simulations provide evidence that greenhouse horticulture businesses display diversity and adaptive complexity, both key features of evolution that led Darwin to develop the theory of natural selection in response to the astounding diversity and adaptive complexity of living species. By showing that non-living entities also possess these same evolutionary hallmarks, this paper provides support for attempts to develop Universal Darwinism, a unified theory of evolution that accounts for both living and non-living natural selection.@en