Formation of calcium oxalate concentric precipitate rings in two-dimensional agar gel systems containing Ca 2+–RE 3+ (RE = Er, Gd and La)–C 2O 42−

Abstract

The concentric precipitate rings are found in urinary stone section and may relate to Liesegang pattern and formation mechanism of urinary stone. Urinary stone is mainly composed of calcium oxalate, so it is significant to study the concentric precipitate rings. The influence of RE 3+ on the formation of calcium oxalate concentric precipitate rings is studied for the first time in two-dimensional agar gel systems. Precipitate rings are characterized by means of Fourier transform infrared spectrometry (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and biomicroscope with digital camera. The results show concentric precipitate rings are made of calcium oxalate and RE 3+ promote the present of rings. The number of concentric rings are influenced by different RE 3+ and the reaction time. The agar gel systems are helpful for the ions to diffuse uniformly, and as a medium where calcium oxalate rings are formed. In comparison with Gd 3+ and La 3+ ions, the content and size of calcium oxalate monohydrate (COM) crystals are highest and biggest after the addition of Er 3+ ions, indicating that Er 3+ ions promote the formation of concentric rings effectively. However, in the similar systems containing Cu 2+, Fe 2+, Fe 3+and Co 2+, we found the ring only appeared in the system containing Fe 3+ ions. And the formation mechanism of the calcium oxalate concentric precipitate rings in two-dimensional agar gel systems containing rare earth ions is also discussed in the paper.