Modified column flotation of adsorbing iron hydroxide colloidal precipitates

Recent advancements in the removal/recovery of toxic metals from aquatic system using flotation techniques

The paramount cause of water scarcity is pollution, which is becoming a massive issue since the last century. Besides, it is evident that water pollution is the main cause of emerging contaminants that are left untreated from industries, can cause serious threats to humans and biota as well. One of the best ways in remediating pollutants and finding a way for generating useable water is to use this contaminated water after the necessary treatment. Heavy metals are of major concern in treatment because of their toxicity, non-biodegradability, carcinogenicity, and they can cause inevitable damages even at low concentrations. In this review article, available different flotation techniques are discussed to address this issue. Flotation tends to be one of the promising techniques that have shown a high scope because of its high produce, low sludge formation, and ease of operation. From the several pieces of literature, it can be inferred that the flotation process can be conducted in one step, and that does not need any expensive materials. Further, this paper deliberates the versatility of each process in disclosing its advantages, limitations, further scope of research and fills the loopholes in the process for better effectiveness. Overall, flotation is a highly probable as well as effective treatment technology to eradicate noxious pollutants present in wastewater and thus helps to compromise environmental and social sustainability.

Removal of Fe(III), Cd(II), and Zn(II) as Hydroxides by Precipitation–Flotation System

In this paper, a combined precipitation–flotation system is proposed for the removal of Fe(III), Zn(II), and Cd(II) as hydroxides. The efficiency of precipitation, as a function of pH, metal ion concentration, and dosage of the precipitating agent as the main variables, was evaluated. The results showed that 99% efficiency was attained from a mixture solution containing the three metal ions in sulfate media at pH 10.3 after 15 min of treatment. The sedimentation behavior showed that a larger precipitate facilitated solid/liquid separation at 30 min. The characterization of precipitates was performed by X-ray diffraction (XRD) identifying iron, zinc, and cadmium oxides; hydroxides; and sodium sulfate. For the flotation, a 20 mg/L solution of dodecylamine (DDA) was used as a collector. Such a solution allowed for the removal of 76% of precipitates in concentrate. An increase in the collector concentration diminished the float percentage due to the micelle formation and low adsorption of the collector on the surface of the precipitate. The results provide evidence of the effectivity of the removal of metal ions by the combined precipitation–flotation system as an alternative for the treatment of acid mine drainage (AMD) in less time in comparison with a sedimentation stage.

Effects of Fe(OH)3 and MnO2 Flocs on Iron/Manganese Removal and Fouling in Aerated Submerged Membrane Systems

Many treatment methods are used to remove iron and manganese from water. Aeration and membrane filtration are two of these methods. In this study, Fe²⁺ and Mn²⁺ removal by aeration with different catalysts and instead of simple membrane filtration applied in other studies, the aerated-submerged membrane systems were evaluated separately. When Fe(OH)₃ was applied in the aeration step and complete oxidation of Fe²⁺ was obtained after 27 min, while complete Mn²⁺ oxidation was obtained in 76 min. However, when MnO₂ was applied in the aeration step, complete oxidation of Fe²⁺ and Mn²⁺ was relatively slow (36 and 110 min, respectively). According to the results obtained from the aerated membrane system, Fe²⁺ and Mn²⁺ removal were extended by Fe(OH)₃ via adsorption/surface oxidation. It is clearly shown from the flux, resistance results, scanning electron microscope (SEM) and Fourier transform infrared (FT/IR) spectroscopy observation that manganese oxides were deposited mainly in membrane pores forming membrane fouling by small flocs, while iron oxide particles were deposited on the membrane surface. Although the flux performance of PT PES membrane was higher than HF PP membrane, fouling resistance of HF PP membrane was higher than PT PES.

Removal of Heavy Metals from Wastewaters: A Challenge from Current Treatment Methods to Nanotechnology Applications

Removing heavy metals from wastewaters is a challenging process that requires constant attention and monitoring, as heavy metals are major wastewater pollutants that are not biodegradable and thus accumulate in the ecosystem. In addition, the persistent nature, toxicity and accumulation of heavy metal ions in the human body have become the driving force for searching new and more efficient water treatment technologies to reduce the concentration of heavy metal in waters. Because the conventional techniques will not be able to keep up with the growing demand for lower heavy metals levels in drinking water and wastewaters, it is becoming increasingly challenging to implement technologically advanced alternative water treatments. Nanotechnology offers a number of advantages compared to other methods. Nanomaterials are more efficient in terms of cost and volume, and many process mechanisms are better and faster at nanoscale. Although nanomaterials have already proved themselves in water technology, there are specific challenges related to their stability, toxicity and recovery, which led to innovations to counteract them. Taking into account the multidisciplinary research of water treatment for the removal of heavy metals, the present review provides an updated report on the main technologies and materials used for the removal of heavy metals with an emphasis on nanoscale materials and processes involved in the heavy metals removal and detection.

Environmental geochemistry and bioaccumulation/bioavailability of uranium in a post-mining context - The Bois-Noirs Limouzat mine (France)

Knowledge on the bioavailability of trace elements is essential in developing environmental quality standards. The purpose of this study was to explore the relationships between trace elements (in particular Uranium (U)) in sediments, porewater and their bioaccumulation by Chironomus riparius on a uranium mining site and river sediments upstream of the mine. The mobility and speciation of U in sediments was investigated using DGT. Geochemical modelling using CHESS provided insight on sorption behavior of U on ironoxyhydrite (HFO) and aqueous speciation of U. In the upstream site U concentrations found were 0.05 μmol g^-1 in surface sediment, 0.84 nmol L^-1 in porewater and 2.4 nmol g^-1 in Chironomus riparius whereas in the ferrihydrite deposits on the mining sites the concentrations found were up to 9.4 μmol g^-1 in surface sediment, 0.37 μmol L^-1 in porewater and 0.684 μmol g^-1 in in Chironomus riparius. Despite the large differences in concentrations of U between the two sites, sediment to dissolved partitioning coefficients, bioconcentration factor (BCF) and biota sediment accumulation factors (BSAF) were very comparable. In the upstream sediment binding of U to organic matter controls sorption and aqueous speciation of U, whereas in the HFO rich sediments, sorption on HFO and the formation of HFO colloids are the determining factors. The low BSAF factors and high BCF factors indicate that the bioaccumulation is due to uptake from the dissolved phase. The DGT probes with different binding resins provide information on the colloidal nature and lability of the dissolved U species.

Correlation between global thermodynamic functions and experimental data in multicomponent heterogeneous systems

The correlation between global thermodynamic functions and such experimental data, which quantitatively characterize the precipitation–dissolution processes of sparingly soluble compounds, as the degree of precipitation and residual concentrations of the solid-phase components in saturated solutions under real conditions, taking into account the complex formation reactions, has been deducted. The paper intends also to introduce widely formal thermodynamic methods for forecasting the conditions of mutual transformation of solid phases through chemical synthesis by precipitation methods, optimization of coprecipitation methods, fractional precipitation from homogeneous solutions, and separation and analysis of chemical compounds. Within the method of residual concentrations, the thermodynamic parameters of the process of precipitating cadmium ions with potassium decanoate from acid and alkaline solutions for different temperatures were investigated. On the basis of the experimentally determined degree of precipitation and its dependence on temperature, the temperature coefficients and overall thermodynamic characteristics of the precipitation process ([Formula: see text], [Formula: see text], and [Formula: see text]) were determined. The optimum conditions of the investigated process of precipitation have been established.

Removal of heavy metal ions from wastewaters: a review

Heavy metal pollution has become one of the most serious environmental problems today. The treatment of heavy metals is of special concern due to their recalcitrance and persistence in the environment. In recent years, various methods for heavy metal removal from wastewater have been extensively studied. This paper reviews the current methods that have been used to treat heavy metal wastewater and evaluates these techniques. These technologies include chemical precipitation, ion-exchange, adsorption, membrane filtration, coagulation-flocculation, flotation and electrochemical methods. About 185 published studies (1988-2010) are reviewed in this paper. It is evident from the literature survey articles that ion-exchange, adsorption and membrane filtration are the most frequently studied for the treatment of heavy metal wastewater.