Precipitation of heavy metals from wastewater using simulated flue gas: sequent additions of fly ash, lime and carbon dioxide

Lime is a preferred precipitant for the removal of heavy metals from industrial wastewater due to its relatively low cost. To reduce heavy metal concentration to an acceptable level for discharge, in this work, fly ash was added as a seed material to enhance lime precipitation and the suspension was exposed to CO2 gas. The fly ash-lime-carbonation treatment increased the particle size of the precipitate and significantly improved sedimentation of sludge and the efficiency of heavy metal removal. The residual concentrations of chromium, copper, lead and zinc in effluents can be reduced to (mg L-1) 0.08, 0.14, 0.03 and 0.45, respectively. Examination of the precipitates by XRD and thermal analysis techniques showed that calcium-heavy metal double hydroxides and carbonates were present. The precipitate agglomerated and hardened naturally, facilitating disposal without the need for additional solidification/stabilization measures prior to landfill. It is suggested that fly ash, lime and CO2, captured directly from flue gas, may have potential as a method for wastewater treatment. This method could allow the ex-situ sequestration of CO2, particularly where flue-gas derived CO2 is available near wastewater treatment facilities. (C) 2009 Elsevier Ltd. All rights reserved.

Characterization of carbonated tricalcium silicate and its sorption capacity for heavy metals: A micron-scale composite adsorbent of active silicate gel and calcite

Adsorption-based processes are widely used in the treatment of dilute metal-bearing wastewaters. The development of versatile, low-cost adsorbents is the subject of continuing interest. This paper examines the preparation, characterization and performance of a micro-scale composite adsorbent composed of silica gel (15.9 w/w%), calcium silicate hydrate gel (8.2 w/w%) and calcite (75.9 w/w%), produced by the accelerated carbonation of tricalcium silicate (C(3)S, Ca(3)SiO(5)). The Ca/Si ratio of calcium silicate hydrate gel (C-S-H) was determined at 0.12 (DTA/TG), 0.17 ((29)Si solid-state MAS/NMR) and 0.18 (SEM/EDS). The metals-retention capacity for selected Cu(II), Pb(II), Zn(II) and Cr(III) was determined by batch and column sorption experiments utilizing nitrate solutions. The effects of metal ion concentration, pH and contact time on binding ability was investigated by kinetic and equilibrium adsorption isotherm studies. The adsorption capacity for Pb(II), Cr(III), Zn(II) and Cu(II) was found to be 94.4 mg/g, 83.0 mg/g, 52.1 mg/g and 31.4 mg/g, respectively. It is concluded that the composite adsorbent has considerable potential for the treatment of industrial wastewater containing heavy metals.

Characterisation of products of tricalcium silicate hydration in the presence of heavy metals

The hydration of tricalcium silicate (C(3)S) in the presence of heavy metal is very important to cement-based solidification/stabilisation (s/s) of waste. In this work, tricalcium silicate pastes and aqueous suspensions doped with nitrate salts of Zn(2+), Pb(2+), Cu(2+) and Cr(3+) were examined at different ages by X-ray powder diffraction (XRD), thermal analysis (DTA/TG) and (29)Si solid-state magic angle spinning/nuclear magnetic resonance (MAS/NMR). It was found that heavy metal doping accelerated C(3)S hydration, even though Zn(2+) doping exhibited a severe retardation effect at an early period of time of C(3)S hydration. Heavy metals retarded the precipitation of portlandite due to the reduction of pH resulted from the hydrolysis of heavy metal ions during C(3)S hydration. The contents of portlandite in the control, Cr(3+)-doped, Cu(2+)-doped, Pb(2+)-doped and Zn(2+)-doped C(3)S pastes aged 28 days were 16.7, 5.5, 5.5, 5.5, and <0.7%, respectively. Heavy metals co-precipitated with calcium as double hydroxides such as (Ca(2)Cr(OH)(7).3H(2)O, Ca(2)(OH)(4)4Cu(OH)(2).2H(2)O and CaZn(2)(OH)(6).2H(2)O). These compounds were identified as crystalline phases in heavy metal doping C(3)S suspensions and amorphous phases in heavy metal doping C(3)S pastes. (29)Si NMR data confirmed that heavy metals promoted the polymerisation of C-S-H gel in 1-year-old of C(3)S pastes. The average numbers of Si in C-S-H gel for the Zn(2+)-doped, Cu(2+)-doped, Cr(3+)-doped, control, and Pb(2+)-doped C(3)S pastes were 5.86, 5.11, 3.66, 3.62, and 3.52. And the corresponding Ca/Si ratios were 1.36, 1.41, 1.56, 1.57 and 1.56, respectively. This study also revealed that the presence of heavy metal facilitated the formation of calcium carbonate during C(3)S hydration process in the presence of carbon dioxide.

Heavy metals in the Fal estuary, Cornwall: A study of long term contamination by mining waste and its effects on estuarine organisms. Occasional Publication of the Marine Biological Association 2

The Fal Estuary System in West Cornwall has, over many centuries, received inputs of heavy metals from various mining activities. In this context its most important tributary is the Carnon River. Analyses of organisms from the Fal Estuary have shown that some species contain abnormally high concentrations of Cu, Zn and As, especially those living in Restronguet Creek.

Marine micro and macro algal species as biosorbents for heavy metals

This paper reviews some practical aspects of the application of algal biomass for the biosorption of heavy metals from wastewater. The ability of different algal species to remove metals varies with algal group and morphology, with the speciation of specific metals and their competition with others in wastewater, and with environmental or process factors. The scattered literature on the uptake of heavy metals by both living and dead algal biomass - both macroalgae and immobilized microalgae - has been reviewed, and the uptake capacity and efficiency of different species, as well as what is known about the mechanisms of biosorption, are presented. Data on metal uptake have commonly been fitted to equilibrium models, such as the Langmuir and Freundlich isotherm models, and the parameters of these models permit the uptake capacity of different algal species under different process conditions to be compared. Higher uptake capacities have been found for brown algae than for red and green algae. Kelps and fucoids are the most important groups of algae used for biosorption of heavy metals, probably because of their abundant cell wall polysacchrides and extracellular polymers. Another important practical aspect is the possibility of re-using algal biomass in several adsorption/desorption cycles (up to 10 have been used with Sargassum spp), and the influence of morphology and environmental conditions on the re-usability of algal tissue is also considered.

Adsorption mechanisms of removing heavy metals and dyes from aqueous solution using date pits solid adsorbent

A potential usefulness of raw date pits as an inexpensive solid adsorbent for methylene blue (MB), copper ion (Cu2+), and cadmium ion (Cd2+) has been demonstrated in this work. This work was conducted to provide fundamental information from the study of equilibrium adsorption isotherms and to investigate the adsorption mechanisms in the adsorption of MB, Cu2+, and Cd2+ onto raw date pits. The fit of two models, namely Langmuir and Freundlich models, to experimental data obtained from the adsorption isotherms was checked. The adsorption capacities of the raw date pits towards MB and both Cu2+ and Cd2+ ions obtained from Langmuir and Freundlich models were found to be 277.8, 35.9, and 39.5 mg g(-1), respectively. Surface functional groups on the raw date pits surface substantially influence the adsorption characteristics of MB, Cu2+, and Cd2+ onto the raw date pits. The Fourier transform infrared spectroscopy (FTIR) studies show clear differences in both absorbances and shapes of the bands and in their locations before and after solute adsorption. Two mechanisms were observed for MB adsorption, hydrogen bonding and electrostatic attraction, while other mechanisms were observed for Cu2+ and Cd2+. For Cu2+, binding two cellulose/lignin units together is the predominant mechanism. For Cd2+. the predominant mechanism is by binding itself using two hydroxyl groups in the cellulose/lignin unit. (C) 2009 Elsevier B.V. All rights reserved.

Hand-held voltammetric analyser for real-time monitoring of heavy metals in situ

This paper presents a novel hand-held instrument capable of real-time in situ detection and identification of heavy metals. The proposed system provides the facilities found in a traditional lab-based instrument in a hand held a design. In contrast to existing commercial systems, it can stand alone without the need of an associated computer. The electrochemical instrument uses anodic stripping voltammetry which is a precise and sensitive analytical method with excellent limits of detection. The sensors comprise disposable screen-printed (solid working) electrodes rather than the more common hanging mercury drop electrodes. The system is reliable, easy to use, safe, avoids expensive and time-consuming procedures and may be used in a variety of situations to help in the fields of environmental assessment and control.

Voltammetric in situ measurements of heavy metals in soil using a portable electrochemical instrument

This paper presents a portable electrochemical instrument capable of detecting and identifying heavy metals in soil, in situ. The instrument has been developed for use in a variety of situations to facilitate contaminated land surveys, avoiding expensive and time-consuming procedures. The system uses differential pulse anodic stripping voltammetry which is a precise and sensitive analytical method with excellent limits of detection. The identification of metals is based on a statistical microprocessor-based method. The instrument is capable of detecting six different toxic metals (lead, cadmium, zinc, nickel, mercury and copper) with good sensitivity