A combined bulk chemistry/electrochemical approach to study the precipitation, deposition and inhibition of CaCO3

State of art bio-materials as scale inhibitors in recirculating cooling water system: a review article

During the operation of the circulating cooling water system, inorganic scale deposition may cause technical problems, such as reduction of heat transfer efficiency in cooling systems and obstruction of pipes. In the industry, chemicals are often used as scale inhibitors in scale deposition control, antiscalants popular in industry are generally phosphorus and nitrogen-containing chemicals, which may lead to eutrophication. However, increasing environmental concern and discharge limitations have guided antiscalants to move toward biodegradability, nontoxicity and cost-effectiveness. This paper reviews current research on the application of using bio-materials as scale inhibitors, including proteins and amino acids, polysaccharides, plant extracts, microbial reagents, and microbiological products. The non-bioaccumulation, low cost, readily biodegradability and sustainably available characters promote the development of green-scale inhibitor chemistry.

The inhibitory effects of four inhibitors on the solution adsorption of CaCO3 on Fe3O4 and Fe2O3 surfaces

This study presents the inhibitory effects of four scale inhibitors, including polyacrylic acid (PAA), hydrolyzed polymaleic anhydride (HPMA), polyepoxysuccinic acid (PESA) and polyaspartic acid (PASP), on the adsorption of CaCO₃ on the surfaces of Fe₃O₄ and Fe₂O₃. Samples were characterized using SEM and EDS and the average atomic number ratios of Ca/Fe were calculated. Inhibition effects followed the trend: PESA > PAA > PASP > HPMA and PESA > PASP > HPMA > PAA for Fe₃O₄ and Fe₂O₃, respectively. Molecular dynamics simulations based on the adsorption model of the scale inhibitor on the surface and calculations of the adsorption energy between the scale inhibitor molecule and the surface revealed that the relatively high scale inhibitory effect is due to low adsorption energy between the inhibitor molecule and the surface. Density Functional Theory (DFT) calculations of the model after adsorption revealed that the relatively low adsorption energy depends on the number of H-O bonds formed as well as those with higher Mulliken population values between the scale inhibitor and the surface.

The inhibition effect mechanisms of four scale inhibitors on the formation and crystal growth of CaCO3 in solution

The experimentation, molecular dynamics simulation and DFT calculation were used to study the inhibition effects of four scale inhibitors, including polyacrylic acid (PAA), hydrolyzed polymaleic anhydride (HPMA), polyepoxysuccinic acid (PESA) and polyaspartic acid (PASP), on formation and crystal growth of CaCO₃ in solutions. According to concentrations of Ca²⁺ in solutions, the sequence of inhibition effects of scale inhibitors on formation of CaCO₃ in the solution was PESA > PASP > HPMA > PAA. Characterization of CaCO₃ crystals by XRD and a laser particle size analyzer indicated that the sequence of inhibition effects of scale inhibitors on crystal growth of CaCO₃ in solutions was PESA > HPMA > PASP > PAA. Interaction energies between the scale inhibitor molecule and Ca²⁺, and between the scale inhibitor molecule and the CaCO₃ (104) surface indicated that the difference of the inhibition effects was derived from the difference in the interaction energy. The results of DFT calculation indicated that the difference between the interaction energies of these inhibitors and Ca²⁺ was derived from differences of number and the Mulliken population values of the chemical bonds which formed between the inhibitor molecule and Ca²⁺ and between the inhibitor molecule and the CaCO₃ surface.

Development of a novel once-through flow visualization technique for kinetic study of bulk and surface scaling

There is a considerable interest to investigate surface crystallization in order to have a full mechanistic understanding of how layers of sparingly soluble salts (scale) build on component surfaces. Despite much recent attention, a suitable methodology to improve on the understanding of the precipitation/deposition systems to enable the construction of an accurate surface deposition kinetic model is still needed. In this work, an experimental flow rig and associated methodology to study mineral scale deposition is developed. The once-through flow rig allows us to follow mineral scale precipitation and surface deposition in situ and in real time. The rig enables us to assess the effects of various parameters such as brine chemistry and scaling indices, temperature, flow rates, and scale inhibitor concentrations on scaling kinetics. Calcium carbonate (CaCO₃) scaling at different values of the saturation ratio (SR) is evaluated using image analysis procedures that enable the assessment of surface coverage, nucleation, and growth of the particles with time. The result for turbidity values measured in the flow cell is zero for all the SR considered. The residence time from the mixing point to the sample is shorter than the induction time for bulk precipitation; therefore, there are no crystals in the bulk solution as the flow passes through the sample. The study shows that surface scaling is not always a result of pre-precipitated crystals in the bulk solution. The technique enables both precipitation and surface deposition of scale to be decoupled and for the surface deposition process to be studied in real time and assessed under constant condition.

Formation of CaCO3 deposits on hard surfaces--effect of bulk solution conditions and surface properties

We have studied nucleation and crystal growth of calcium carbonate on hard surfaces, i.e. stainless steel and silica, at different temperatures, in relation to the corresponding bulk processes, using scanning electron microscopy (SEM), X-ray diffraction (XRD), and ellipsometry. In the bulk solution, a mixture of all three calcium carbonate crystalline polymorphs, calcite, aragonite, and vaterite, as well as amorphous particles was observed at 25 °C, while at 55 °C aragonite and calcite crystals dominated. On surfaces only calcite crystals were observed at 25 °C, whereas aragonite and calcite crystal adsorbed on the surfaces at 55 °C. Two kinds of nucleation and adsorption mechanism of CaCO3 crystals on hard surfaces were observed, depending on the surface orientation (vertical or horizontal, i.e., subject to sedimentation) in the bulk solution. A model for the relation between interfacial layer structure, the substrate, and the solution crystallization is discussed based on the observed difference in deposition between type of surfaces and surface orientation. In addition, the effect of magnesium ion on the morphology of calcium carbonate crystals is discussed.