			Home About us Contact

Leaching Process (leaching + process)

Distribution by Scientific Domains

Engineering	55%
Chemistry	33%

Selected Abstracts

Treatment of Process Water Containing Heavy Metals with a Two-Stage Electrolysis Procedure in a Membrane Electrolysis Cell

ENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 2 2005
R. Fischer
Abstract The capability of a two-stage electrochemical treatment for the regeneration of acidic heavy-metal containing process water was examined. The process water came from sediment bioleaching and was characterized by a wide spectrum of dissolved metals, a high sulfate content, and a pH of about 3. In the modular laboratory model cell used, the anode chamber and the cathode chamber were separated by a central chamber fitted with an ion exchanger membrane on either side. The experiments were carried out applying a platinum anode and a graphite cathode at a current density of 0.1,A/cm2. The circulation flow of the process water in the batch process amounted to 35,L/h, the electrolysis duration was 5.5,h at maximum and the total electrolysis current was about 1,A. In the first stage, the acidic process water containing metals passed through the cathode chamber. In the second stage, the cathodically pretreated process water was electrolyzed anodically. In the cathode chamber the main load of dissolved Cu, Zn, Cr and Pb was eliminated. The sulfuric acid surplus of 3,4,g/L decreased to about 1,g/L, the pH rose from initially 3.0 to 4,5, but the desired pH of 9,10 was not achieved. Precipitation in the proximity to the cathode evidently takes place at a higher pH than farther away. The dominant process in the anode chamber was the precipitation of amorphous MnO2 owing to the oxidation of dissolved Mn(II). The further depletion of the remaining heavy metals in the cathodically pretreated process water by subsequent anodic treatment was nearly exhaustive, more than 99,% of Cd, Cr, Cu, Mn, Ni, Pb, and Zn were removed from the leachate. The high depletion of heavy metals might be due to both the sorption on MnO2 precipitates and/or basic ferrous sulfate formed anodically, and the migration of metal ions through the cation exchanger membrane via the middle chamber into the cathode chamber. In the anode chamber, the sulfuric acid content increased to 6,7,g/L and the pH sank to 1.7. All heavy metals contained, with the exception of Zn, were removed to levels below the German limits for discharging industrial wastewaters into the receiving water. Moreover, the metal-depleted and acid-enriched process waters could be returned to the leaching process, hence reducing the output of wastewater. The results indicated that heavy metals could be removed from acidic process waters by two-stage electrochemical treatment to a large extent. However, to improve the efficiency of metal removal and to establish the electrochemical treatment in practice, further work is necessary to optimize the operation of the process with respect to current density, energy consumption, discharging of metal precipitates deposited in the electrode chambers and preventing membrane clogging. [source]

A study of copper recovery from copper-contaminated sludge with ferrite and selective leaching processes

ENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 1 2007
S.H. Hu
Abstract The purpose of this study was to develop an effective resource recovery and leached residue stabilization process for copper-contaminated sludge. To this end, a treatment procedure utilizing ferrite and selective leaching processes was developed. The XRD examination of ferrite complex revealed the crystalline phases to be mainly Fe3O4, CuO, and 6CuO·Cu2O. A selective leaching process was followed to recover the copper content of the ferrite complex. To promote the dissolution percentage of copper and repress that of iron, additional 0.5 N sulfuric acid was added at intervals to the suspension in the second step of the selective leaching process. The purpose of this operation was to return the suspension pH back to 3 to promote the dissolution of copper oxide and repress the dissolution of iron. Finally, the heavy metal (i.e., Cu, Pb, Cr, and Cd) dissolution of the above residue was examined with toxicity characteristic leaching procedure (TCLP) testing and all met the regulatory standard. © 2007 American Institute of Chemical Engineers Environ Prog 26:104,112, 2007 [source]

Alkaline leaching of printed circuit board sludge

ENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 3 2006
S.H. Hu
Abstract The purpose of this study was to develop a treatment procedure for processing aluminum-contaminated sludge produced from the coagulation/flocculation process of wastewater treatment in the manufacture of printed circuit boards (PCBs). In this study, the reagent sodium hydroxide (2 N) was used to leach the heavy metal sludge and the dissolution of sludge's aluminum content was roughly 70%. The weight loss of the heavy metal sludge was caused by the dissolution of aluminum content of nearly 20%. Although dissolution of a small amount of copper occurred simultaneously during this leaching process, the dissolution of copper content was restricted within 0.72% in the leaching operation and the copper content was concentrated in the residue to increase the copper level. The large amounts of sodium hydroxide and Al3+ remaining in the leachate were recycled as neutralization and coagulation agents in wastewater treatment. Synthetic heavy metal wastewater was neutralized with the preceding leachate to estimate the reuse feasibility of recovered coagulant. The heavy metal concentration of the effluent met regulation standards after neutralization and precipitation. The settling rate could be significantly enhanced by the addition of 100 ppm supplemental polyacrylamide (PAM). © 2006 American Institute of Chemical Engineers Environ Prog, 2006 [source]

Using a pore-scale model to quantify the effect of particle re-arrangement on pore structure and hydraulic properties

HYDROLOGICAL PROCESSES, Issue 8 2007
Oagile Dikinya
Abstract A pore-scale model based on measured particle size distributions has been used to quantify the changes in pore space geometry of packed soil columns resulting from a dilution in electrolyte concentration from 500 to 1 mmol l,1 NaCl during leaching. This was applied to examine the effects of particle release and re-deposition on pore structure and hydraulic properties. Two different soils, an agricultural soil and a mining residue, were investigated with respect to the change in hydraulic properties. The mining residue was much more affected by this process with the water saturated hydraulic conductivity decreasing to 0·4% of the initial value and the air-entry value changing from 20 to 50 cm. For agricultural soil, there was little detectable shift in the water retention curve but the saturated hydraulic conductivity decreased to 8·5% of the initial value. This was attributed to localized pore clogging (similar to a surface seal) affecting hydraulic conductivity, but not the microscopically measured pore-size distribution or water retention. We modelled the soil structure at the pore scale to explain the different responses of the two soils to the experimental conditions. The size of the pores was determined as a function of deposited clay particles. The modal pore size of the agricultural soil as indicated by the constant water retention curve was 45 µm and was not affected by the leaching process. In the case of the mining residue, the mode changed from 75 to 45 µm. This reduction of pore size corresponds to an increase of capillary forces that is related to the measured shift of the water retention curve. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Kinetics of Solids Leaching During Rehydration of Particulate Dry Vegetables

JOURNAL OF FOOD SCIENCE, Issue 3 2004
A. MARABI
ABSTRACT: Air-dried and freeze-dried carrots were rehydrated in a computerized mixing system, and the medium was analyzed for sugar content with high-performance liquid chromatography (HPLC) and for total organic carbon (TOC). Leaching of solids was significant at very short rehydration time. Understanding the mechanism of the leaching process could provide information required for simulation. TOC values were significantly higher than those derived by HPLC, indicating that other organic components were extracted. The difference between TOC and HPLC values varied with time, indicating the existence of a different mass transfer rate. Sugars and TOC values followed an exponential behavior. Quantifying solids leaching is important for modeling and simulation of the rehydration process and for product optimization. [source]

Electric-oxidation kinetics of molybdenite concentrate in acidic NaCl solution

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2009
Cao Zhan-fang
Abstract The electric-oxidation kinetics of molybdenite concentrate in NaCl electrolyte was investigated in this study. The effects of liquid-to-solid ratio, stirring speed, and concentration of NaCl on the dissolution rate were determined. It was found that the dissolution rate increases with increase in liquid-to-solid ratio, stirring speed, and concentration of NaCl. A shrinking particle model is presented to describe the dissolution and to analyse the data. The apparent activation energy of this dissolution process was found to be 8.2,kJ/mol; it was established that the leaching process is mainly controlled by diffusion, and the kinetics formula of this research system can be expressed as: . Dans cette étude, on examine la cinétique de l'oxydation électrique d'un concentré de molybdénite dans un électrolyte de NaCl. Les effets du rapport liquide-solide, de la vitesse d'agitation et de la concentration de NaCl sur le taux de dissolution ont été déterminés. Il a été découvert que le taux de dissolution augmente avec le rapport liquide-solide, la vitesse d'agitation et la concentration de NaCl. Un modèle de contraction de particule est présenté pour décrire la dissolution et analyser les données. L'énergie d'activation apparente de ce processus de dissolution a été évaluée à 8,2KJ/mol. Il a été établi que le processus de lixiviation est principalement contrôlé par diffusion et la formule cinétique de ce système de recherche peut être exprimée sous la forme: k,=,0,0207C exp(,8200/RT). [source]

A study of copper recovery from copper-contaminated sludge with ferrite and selective leaching processes

Managing nitrogen on the farm: the devil is in the detail,

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 4 2007
Mark Shepherd
Abstract Agricultural activity is a major source of nitrate in surface and ground waters. There has been a large research effort over the last 20 years to understand nitrate leaching processes and to develop ,best management practices' (BMPs) that can be adopted in farming systems to reduce losses to the wider environment. This paper reviews some of the issues relating to the development, use and adoption of these BMPs in farming systems. There is significant evidence from farming systems experiments and modelling studies that combinations of BMPs can decrease nitrate losses from agricultural land, though nothing is foolproof (the weather plays a key role in determining success). The challenges are greater in some regions (dry climate, ,leaky' soils) and in some enterprises (intensive animal farming systems). The adoption of BMPs on farms requires attention to detail and a high level of management skill, so providing advisory support to farmers is essential. Even with the progress that has been made in recent years, there is still work to do. This includes encouraging uptake on farms and dealing with potential conflicts between BMPs when they create ,pollution swapping' or where there is potential for a large economic penalty for the farmer. We also suggest that there is a need for more innovation in developing BMPs and a need to recognise that, in some situations, radical changes to farming systems may be the only solution. Copyright © 2007 Society of Chemical Industry [source]