《Hydrometallurgy》2007,87(3-4):178-190

The hydrolysis of ferric iron at elevated temperatures and pH values between 1.5 and 3.5 was characterized by determining the stability regions for schwertmannite, 6-line ferrihydrite and 2-line ferrihydrite, and linking them to the supersaturation levels present during their formation. It was shown that most industrial iron removal processes are operated above the metastability limit. However, stagewise precipitation of iron, even above the metastability limit, yielded better quality precipitates. Furthermore, careful selection and control of pH and temperature are required to improve product quality expressed in terms of the solids impurity content, dry solids density, particle size and the particle number density.  相似文献   

    

《Metal Powder Report》2014,69(6):3

  相似文献   

    

《Water research》1996,30(3):511-520

The objective of this research was identification of optimal surfactant systems for remediating chromate-contaminated subsurface environments. Batch and column studies were conducted utilizing chromium contaminated soil obtained from the U.S. Coast Guard Support Center, Elizabeth City, N.C. Results of the batch studies demonstrated that surfactants, when used alone, were able to enhance the extraction of chromate 2.0–2.5 times greater than water. When a complexing agent, diphenyl carbazide, was solubilized by aqueous micelles the system was able to enhance the chromate elution by 9.3 to 12.0 times greater than water (or 3.7–5.7 times greater than surfactant without the complexing agent). Column studies showed that when surfactants are used along with the complexing agent, 213% of Cr(VI) can be removed relative to D.I. water in less than 20 pore volumes, whereas D.I. water took 35 pore volumes to reach the baseline removal. The economics of surfactant enhanced subsurface remediation will be affected by surfactant losses (e.g. precipitation and sorption); batch and column studies were conducted to evaluate the losses of surfactants due to such phenomena. Results of these laboratory studies demonstrated that the surfactant system containing Dowfax 8390 and diphenyl carbazide was most effective in remediation of the chromium contaminated soil.  相似文献   

    

Frank Vanclay  Dr Lorraine Elliott 《影响评估与项目评价》2013,31(2):167-169

The environmental impact assessment (EIA) system in Uzbekistan was inherited from the USSR and is centred on state environmental review, a procedure for reviewing the impacts of proposed activities by environmental authorities. This is proving to be a less effective tool of environmental protection in the new political and economic conditions. Since the collapse of the USSR, the Uzbekistani EIA system has undergone gradual reform but the national EIA system remains almost identical to the ‘socialist’ system. At the same time, some elements are similar to those of EIA systems used in developed countries. The shortcomings of the system include unclear screening provisions and lack of public participation. The paper analyses strengths, weaknesses, opportunities and threats for the development of EIA in Uzbekistan, taking into account various political and economic factors.  相似文献   

    

《Materials Letters》2006,60(21-22):2711-2714

Anatase phase, three-dimensionally ordered macroporous (3 DOM) Ti_1−xTa_xO_{2 + x / 2} (x = 0.025, 0.05, and 0.075) nanoparticles with macropore diameter 290 to 310 nm, wall thickness 50 to 80 nm, and particle size 10 to 12 nm were prepared by combination of the sol–gel chemistry and polystyrene (PS) templating procedure. The products exhibited relatively narrower band gaps and larger BET surface areas than those of the starting solitary 3 DOM metal oxides, and their photocatalytic activities for the degradation of an aqueous 4-nitrophenol remarkably enhanced compared with 3 DOM anatase TiO₂, Ta₂O₅, and Degussa P-25.  相似文献   

    

Rachel L. Roberts  Torsten Schwich  T. Christopher Corkery  Marie P. Cifuentes  Katy A. Green  Julian D. Farmer  Paul J. Low  Todd B. Marder  Marek Samoc  Mark G. Humphrey 《Advanced materials (Deerfield Beach, Fla.)》2009,21(22):2318-2322

  相似文献   

    

《Cement and Concrete Composites》1999,21(4):285-291

In cementitious binders when used for masonry mortars the requirements for properties of importance during early and later ages are different. Whereas during the early periods the attributes required are water retention, workability, plasticity, adhesion, etc. to allow the mortar to possess good working properties such as the ease of spreading, proper filling of joints and also to provide a water resistant crack free smooth surface, but at later ages strength becomes the main criterion to sustain the imposed load of the structure. Portland cement based mortars though harden rapidly and attain high strength but possesses a relatively poor early age properties. In composite mortars there is a common practice to incorporate lime along with portland cement, whose presence improves upon the early age rehological properties. Once the setting and hardening take place and the role of these early age properties is completed, lime has little role to play, as it harden through the lethargic process of carbonation i.e. by the chemical action of lime with atmospheric carbon dioxide forming insoluble carbonate. The process of carbonation is very slow and takes place from surface inwards. Modified composite mortars have been developed by the replacement of certain part of lime with pozzolana such as burnt clay or flyash and has been found to be of advantage. Laboratory investigations on a series of such mixtures have revealed the possession of good early age properties and at the same time better strength at later ages. Some of the results are reported in this paper.  相似文献   

    

《Materials Letters》2005,59(14-15):1954-1957

An analytical approach to compute the effective elastic moduli of syntactic foams is presented. Using the concentric spherical model, the effective elastic constants are estimated, and compared with other theories and experimental data. The computed effective elastic moduli are within the lower and upper bounds, and agree with the experimental data.  相似文献   

    

《Composites Science and Technology》2006,66(3-4):538-547

The present paper summarizes an experimental study on the mechanical and viscoelastic behavior of jute fibre reinforced high density polyethylene (HDPE) composites. Variations in mechanical strength, storage modulus (E′), loss modulus (E″) and damping parameter (tan δ) with the addition of fibres and coupling agents were investigated. It was observed that the tensile, flexural and impact strengths increased with the increase in fibre loading upto 30%, above which there was a significant deterioration in the mechanical strength. Further, the composites treated with MAPE showed improved properties in comparison to the untreated composites. Dynamic mechanical analysis data showed an increase in the storage modulus of the treated composites The tan δ spectra presented a strong influence of fibre content and coupling agent on the α and γ relaxation process of HDPE. The thermal behavior of the composites was evaluated from TGA/DTG thermograms. The fibre–matrix morphology in the treated composites was confirmed by SEM analysis of the tensile fractured specimens. FTIR spectra of the treated and untreated jute fibres was also studied to ascertain the existence of type of interfacial bonds.  相似文献   

    

《Composites Science and Technology》1988,31(2):121-141

A survey has been carried out on thetensile strength and toughness of a wide variety of fibre reinforced composites containing several different types of constituents and of many kinds of lay-up. It is shown that there is a simple linear relationship between the strength and the property we refer to as the critical stress intensity factor, K_IC. The implication is that all composites appear to behave as though they contained a defect of the order of 1 mm in length, no matter what their structure or composition. This appears to be an unlikely possibility, and it is concluded that the use of a concept such as critical stress intensity has no meaning for such materials on account of their complex structure and cracking patterns.  相似文献