The solubility and stability of calcium arsenates at 25 • C was determined by both precipitation and dissolution experiments. Ca 3 (AsO 4 ) 2 ·3H 2 O(c), Ca 3 (AsO 4 ) 2 ·2 1 / 4 H 2 O(c), Ca 5 (AsO 4 ) 3 (OH)(c) and Ca 4 (OH) 2 (AsO 4 ) 2 ·4H 2 O(c) were identified in our experiment over a wide range of pH and for Ca/As molar ratios between 1.25 and 4.0. The solids precipitated at pH = 3 ∼ 7 and Ca/As = 1.5 were phase-pure and well-crystallized Ca 3 (AsO 4 ) 2 ·xH 2 O(c) and had relatively larger grain size than those formed at pH > 7. Based on the analytical results and using the computer program PHREEQC, the solubility products for Ca 3 (AsO 4 ) 2 ·3H 2 O(c), Ca 3 (AsO 4 ) 2 ·2 1 / 4 H 2 O(c), Ca 5 (AsO 4 ) 3 (OH)(c) and Ca 4 (OH) 2 (AsO 4 ) 2 ·4H 2 O(c) were calculated as K sp of 10 −), respectively. Correspondingly, the free energies of forming ( G o f ) of these calcium arsenates were calculated to be −3787.87 kJ/mol, −3611.50 kJ/mol, −5096.47 kJ/mol and −4928.86 kJ/mol.

Vacuum diffusion bonding of stainless steel to copper was carried out at a temperature ranging from 830 to 950°C under an axial pressure of 3 MPa for 60 min with three kinds of interlayer metals: tin-bronze (TB) foil, Au foil, and TB-Au composite interlayer. The results showed that the grain boundary wetting was formed within the steel adjacent to the interface due to the contact melting between TB and Au when TB-Au composite interlayer was used. The grain boundary wetting could occur at a relatively low temperature of 830°C and becomes significant with the increase of temperature. The tensile strength of the joint with TB-Au was higher than that with TB or Au interlayer separately and could be 228 MPa at the joining temperature of 850°C. Furthermore, the axial compression ratio of the specimen joined at 850°C was approximately 1.2%. Therefore, a reliable and precise joining of stainless steel to copper could be realized by diffusion bonding with the TB-Au composite interlayer at a comparatively low temperature.

Pollution of heavy metals has become a serious environmental problem and it needs to be solved as soon as possible. Diatomite is a kind of biogenic rock and it is siliceous and sedimentary. There is abundant diatomite resource in China. Diatomite has distinctive structure of diatom monoblock. It has strong adsorbability, its specific area is large and it has high porosity. Its surface adheres a lot of active groups and negative charge. Diatomite with proper modification would show outstanding absorption effect of heavy metal ions. This paper reviewed the absorption efficiency of heavy metal ions on diatomite modified by metallic oxide, acids and bases, acticarbon, calcium carbonate and organics, the results would offer references for related researches. At last, this paper takes the outlook for the modified methods and application prospects of diatomite in wastewater treatment of heavy metals.

In this study, calcium carbonate was used to coat and link the surface of diatomite for the formation of a novel modified adsorbent (referred to as Ca–diatomite). Various analytical techniques were used to characterize structure and mechanisms of modification and adsorption process, like Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD). Results showed that that Calcium carbonate had been successful grafted onto the surface of diatomite after modification, and Calcium carbonate modification improved the adsorption performance of diatomite for the removal of lead (II) ions from aqueous solution. Ca–diatomite adsorption isotherms and adsorption kinetics were also been studied. The adsorption isotherms and the kinetic data were best fitted with the Langmuir model and pseudo-second-order kinetics, respectively.

Owing to the efficient predetermination, specific recognition and wide applicability, metal ion imprinting technology, apply to the wastewater treatment. The principles, synthesis strategies of ion imprinting and typical heavy metal ion imprinted polymers (IIPs) are introduced in the review. Finally, it is pointed out that the futures research problems to be solved and the development direction of metal ion imprinting technology.