Sand consolidation with calcium phosphate–polyelectrolyte composites

A new method for the consolidation of loose sand formations has been developed. The method involves in situ precipitation of a composite calcium phosphate–polyelectrolyte salt that binds together with loose sand grains, thus resulting to their consolidation. Three different polyelectrolytes (PE) were tested, i.e., polyacrylic acid (PAA), polyallylamine hydrochloride (PAH), and polyethylenimine (PEI). The effect of PE tested on the thermodynamics and the kinetics of precipitation of calcium phosphate salts was investigated. Three types of experiments were done. Investigation of the adsorption of PE on either hydroxyapatite (Ca5(PO4)3OH, HAP) crystals or on sand grains. Measurement of the kinetics of heterogeneous nucleation of HAP on the solid substrates and the mechanical properties of the obtained crystals in batch experiments of low and high supersaturation solutions, respectively. Evaluation of the consolidation in sand packs in order to investigate the effectiveness of the method. The crystallization rates, Rp, on HAP crystals in the presence of the PE tested were found in the order RpPAA>RpPEI>RpPAH, while nucleation and crystal growth on silicate sand took place only in the absence of adsorbed PE. PAH favored strongly the consolidation process, whereas PEI and PAA resulted in the formation of poorly consolidated grain agglomerates.

Uniform coverage of sand grain surface by a thick layer of OCP crystals.Figure optionsDownload high-quality image (53 K)Download as PowerPoint slideHighlights
► Composite solids of salts–polymers consolidated satisfactorily loose sand grains.
► Adsorption of polymers on salts was found to be pH and ionic strength dependent.
► Polymers influenced the kinetics and the morphology of mineral phase deposited.
► The compressive strength of the composite solids reached values as high as 60 MPa.
► Presence of a polymer in sandbed experiments increased the compressive strength.