3D numerical investigation of thermally assisted high efficiency ductile machining of nanocrystalline hydroxyapatite

This study investigates the effects of four different variables (initial workpiece temperature, side rake angle, edge radius/feed rate, and nose radius/depth of cut) on ductile regime machining of a bioceramic material known as nanohydroxyapatite (nano-HAP) using 3D numerical simulation. AdvantEdge FEM Version 5.9 is used to conduct turning simulations of the nano-HAP workpiece. Tecplot 360 is used to analyze the results of the simulations. Because the workpiece is thin, the entire workpiece is set to a uniform initial temperature to simulate laser preheating of the material. Initial workpiece temperature, rake angle (side rake angle), edge radius, and nose radius are varied, and the effects of these operating conditions on critical feed are investigated. It is found that critical feed increases as initial workpiece temperature increases, and also as negativity of rake angle increases. For the edge radius, it is concluded that an initial increase causes an increase in critical feed – however, at some value of edge radius, critical feed shows no further increase; for the nose radius, critical feed appears to show no significant dependence.     

Evaluation of the effectiveness of phosphate treatment for the remediation of mine waste soils contaminated with Cd, Cu, Pb, and Zn

The effectiveness of phosphate treatment for Cd, Cu, Pb, and Zn immobilization in mine waste soils was examined using batch conditions. Application of synthetic hydroxyapatite (HA) and natural phosphate rock (FAP) effectively reduced the heavy metal water solubility generally by about 84-99%. The results showed that HA was slightly superior to FAP for immobilizing heavy metals. The possible mechanisms for heavy metal immobilization in the soil involve both surface complexation of the metal ions on the phosphate grains and partial dissolution of the phosphate amendments and precipitation of heavy metal-containing phosphates. HA and FAP could significantly reduce Cd, Cu, Pb, and Zn availability in terms of water solubility in contaminated soils while minimizing soil acidification and potential risk of eutrophication associated with the application of highly soluble phosphate sources.     

Screening hydroxyapatite for cadmium and lead immobilization in aqueous solution and contaminated soil: The role of surface area

Hydroxyapatite (HAP) has been widely used to immobilize many cationic metals in water and soils. The specific reason why an increase in the surface area of HAP enhances cadmium (Cd) uptake, but has no effect on lead (Pb) uptake, is not clear. The aim of this study was to determine the factors causing the differences in sorption behavior between Cd and Pb by evaluating HAPs with different surface areas. We synthesized HAPs with two different surface areas, which were characterized by X-ray diffraction, N₂ adsorption, and scanning electron microscopy, and then evaluated them as sorbents for Cd and Pb removal by testing in single and binary systems. The sorption capacity of large surface area HAP (1.85 mmol/g) for Cd in the single-metal system was higher than that of small surface area HAP (0.64 mmol/g), but there were no differences between single- and binary-metal solutions containing Pb. After the Cd experiments, the HAP retained a stable structure and intact morphology, which promotes the accessibility of reactive sites for Cd. However, a newly formed precipitate covered the surface and blocked the channels in the presence of Pb, which reduced the number of potential adsorption sites on HAP for Cd and Pb. Remediation experiments using Cd- and Pb-contaminated soil produced similar results to the solution tests. These results indicate that alterations of the structure and morphology during the reaction is an important factor influencing metal sorption to HAP.     

HAP/UV催化降解活性艳蓝K-3R的研究

用化学沉淀法合成羟基磷灰石(HAP),并用XRD、SEM、FT-IR对其进行分析。以活性艳蓝K-3R为降解底物,研究HAP对其光催化降解性能。探讨了HAP煅烧温度、通气量、投加量、初始浓度等因素对光催化降解活性艳蓝K-3R效果的影响。研究表明化学沉淀法合成的HAP粒度均匀,HAP对活性艳蓝的吸附作用较强,30min之内即能达到吸附平衡,其对初始浓度为100mg/L的活性艳蓝的吸附率可达17.5%。适当的煅烧有利于提高HAP的催化活性,以200℃煅烧2h最佳。在投加量为4g/L,鼓气量为300L/h和pH=6的试验条件下,HAP(200℃)对初始浓度为100mg/L的活性艳蓝K-3R 3h的降解率达68%。降解反应动力学研究表明,HAP/UV光催化降解活性艳蓝K-3R的过程符合Langmuir-Hinshel-wood一级动力学方程,降解速率常数k随着活性艳蓝K-3R浓度的增大而减小。     

Synthesis of hydroxyapatite/clay and hydroxyapatite/pumice composites for tetracycline removal from aqueous solutions

Synthesized hydroxyapatite/clay (HA-C) and hydroxyapatite/pumice (HA-P) composites were used for tetracycline (TC) uptake studies from aqueous solution and their uptake capacities were compared. HA-C and HA-P composites were synthesized by precipitation method and the structures of the synthesized composites were characterized by XRD, SEM and BET analyses. Cation exchange capacities of HA-C and HA-P were found to be 84 meq/100 g and 33 meq/100 g, respectively. The TC adsorption using HA-C and HA-P was studied on batch mode. Various parameters such as contact time, solution pH, initial TC concentration, composite dosage, salinity and temperature were optimized. Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models were applied to the equilibrium data. The maximum adsorption capacity onto HA-C was found to be 76.02 mg/g and about four times larger than the adsorption capacity of the HA-P (17.87 mg/g). The results indicated that the TC uptake onto HA-C and HA-P composites is mainly by a surface complexation and ion-exchange mechanism which depend on the solution pH. The calculated values of thermodynamic parameters indicated that the TC adsorption is favorable, physicochemical in nature. The sorption process follows pseudo-second-order and intraparticle diffusion kinetic models. The TC adsorption mechanism by HA-C and HA-P has been proposed.