Heated blends of phosphate waste: Microstructure characterization, effects of processing factors and use as a phosphorus source for alfalfa growth.

Microstructure of expandable lightweight aggregates (LWAs), which was composed of phosphate waste (PW), cement kiln dust (CKD) and raw clay (RC) was investigated, and the effects of processing factors (temperature, waste content, soaking time) on their physical properties were quantified by using response surface methodology (RSM). The potential use of LWAs as a phosphorus source was assessed through the use of seeds of alfalfa. It was found that the main minerals of the waste, namely carbonates and fluorapatite, were involved in the formation of labradorite/anorthite and melt respectively. Stability of mullite- the main constituent of CKD- was sensitive to the melt content. The assemblage of the identified phases was discussed based on the CaO-SiO2-Al2O3 phase diagram. The results of RSM showed that the change of compressive strength, firing shrinkage and water absorption of LWAs versus processing factors was well described with a polynomial model and the weights of the effects of the factors increased in the following order: sintering temperature > waste content (in the case of PW-RC) > soaking time. On the other hand, it was found that due to the release of phosphorus by soil-embedded pellets, the growth of alfalfa plants improved, and the rate enhanced in this order: PW-RC > PW-CKD > PW-CKD-RC. The absorbed quantity of phosphorus (0.12%) was still lower than the common uptake amount.

Phosphate sludge: thermal transformation and use as lightweight aggregate material.

Phosphate sludge generated from beneficiation plants of Moroccan phosphate rocks was investigated at 900-1200 °C by X-ray diffraction, scanning electron microscopy, thermal analysis and Fourier-transform infrared spectroscopy. Mixtures of the phosphate sludge and a swelling clay (up to 30 wt.%) were investigated and their properties (shrinkage, density, water absorption and compressive strength) were measured as a function of temperature and clay addition. The results showed that gehlenite neoformed from lime of decomposed carbonates and breakdown products of clay minerals and that fluorapatite (original mineral) resisted heating until fusion. The measured properties were mainly controlled by temperature, and the effect of clay addition was less regular, except for water absorption. Considering the mixtures densities (1.44-3.02 g/cm(3)), lightweight agglomerates can be produced at 900 or 1100 °C, but their compressive strengths were relatively low (2-4.5 MPa). Based on SiO2-Al2O3-Fluxes diagram and taking account of the chemical composition of the materials used, the production of expanded aggregates requires clay additions as high as 80 wt.%.

Temperature-dependent neutron powder diffraction evidence for splitting of the cationic sites in ferroelectric PbHf0.4Ti0.6O3.

Temperature-dependent neutron powder diffraction experiments (diffractometer 3T2-LLB, Saclay, France, lambda = 1.227 Å) have been performed on the perovskite-like lead hafnate titanate PbHf(0.4)Ti(0.6)O(3). This compound belongs to the solid solution denoted PHT, which derives from the well known ferroelectric PZT series. It exhibits a ferroelectric-to-paraelectric phase transition around 620 K, between the low-temperature tetragonal phase and the high-temperature cubic phase. The tetragonal structure of the ferroelectric phase has been refined at 10 and 300 K using a Rietveld-type method: space group P4mm with Z = 1; a(t) = 3.999 (1), c(t) = 4.120 (1) Å, c/a = 1.030, V = 65.89 Å(3) at 10 K; a(t) = 4.012 (1) and c(t) = 4.100 (1) Å, c/a = 1.022, V = 65.99 Å(3) at 300 K. The cubic structure of the paraelectric phase has also been refined at 720 K: space group Pm3;m, Z = 1, a(c) = 4.046 (1) Å, V = 66.23 Å(3). Cation displacements and oxygen-octahedra elongations have been observed as a function of temperature. Evidence for peculiar behaviour associated with the relative shifts of the Hf and Ti atoms (thought until now to be on the same crystallographic site) was found through an anomaly of the mean-square atomic displacements of the Hf/Ti pseudo-nucleus. The PDF Nos for PbHf(0.4)Ti(0.6)O(3) are 48-49-9 and 48-49-10.