An Electrokinetic Process Coupled Activated Carbon Barrier for Nickel Removal from Kaolinite

Electrokinetic (EK) remediation coupled with activated carbon barrier was evaluated to remove nickel (500 mg/kg) from kaolinite. Laboratory experiments were performed by applying a constant voltage to create electric field strength of 1 or 1.25 V/cm for 3 days. Findings showed that the barrier filled with activated carbon could prevent the formation of reverse electro-osmotic flow, which had an adverse effect on the Ni(II) removal. Application of activated carbon barrier into EK process resulted in an increase of Ni migration from 11 to 47%

Response to the comments of Zhang et al.(2014) on “Heavy metals and polycyclic aro-matic hydrocarbons: Pollution and ecologicalrisk assessment in street dust of Tehran”

Before the Saeedi et al. [3] publication, RI has been employed for ecological risk assessment of heavy metals in soil and dust samples in several studies [4–9]. It has also been employed by researchers after this publication [10–15]. This shows that many researchers accept the view that RI is an appropriate and useful risk assessment index for some environments other than aquatic environment such as terrestrial one. However, the issues raised by Zhang et al. [1] could have been discussed and explained in our manuscrip

Mechanical activation for sulfidic tailings treatment by tailings: Environmental aspects and cement consumption reduction

Sulfidic mine tailings are one of the massive hazardous solid wastes, containing large amounts of toxic heavy metals. Poor management of tailings can lead to the production of acid mine drainage and the heavy metal transfer emissions into the environment. Thus, in this study, mechanical activation was used to reuse a combination of carbonate tailings (TC) and sulfidic tailings (TS) for concrete construction purposes and to effectively immobilize heavy metals. The results showed that after tailings treatment, the heavy metal leaching rate was significantly below the allowed criteria based on the toxicity characteristic leaching procedure (TCLP). The mercury intrusion porosimetry (MIP) test results on the specific surface area and porosity after the activation pointed out increase and reduction, respectively. In the concrete sample containing 20 % cement-replacing activated tailings, the critical pore diameter after 28 curing days was 60 nm, which was less than that of the control sample with a critical pore diameter of 150 nm. According to X-ray diffraction (XRD) and scanning electron microscopy (SEM), ettringite and calcium silicate hydrate gel acted as hosts for heavy metals ions and played an inevitable role in stabilizing metal pollutants. Results revealed that the compressive strength of the sample containing 20 % of the activated tailings after 28 curing days was 31.2 MPa, which was higher than the strength of the control sample (26.99 MPa). Overall, it was concluded that the combined mechanically activated mine tailings can be a viable substitute for cement (up to 40 %) for constructing concrete samples. The utilized combined approach led to diminish adverse effect of sulfide content in concrete samples besides the cement consumption reduction

Simultaneous Removal of Cyanide and Heavy Metals Using Photoelectrocoagulation

One of the new methods used to remove the contaminants from effluent is the electrocoagulation method, which is sometimes combined with other methods to increase the removal efficiency of contaminants. To simultaneously remove nickel, cyanide, zinc, and copper, the combined method of photo-electrocoagulation was used along with an oxidizing agent, namely hydrogen peroxide (Hp). In addition, the effects of factors affecting the removal efficiency were studied, including pH, electrode arrangement, and current intensity. An electric current of 300 mA at a pH of 10 for 60 min, Fe-SS electrodes with a distance between them of 5 cm, and hydrogen peroxide at a rate of 4 mg/L were the ideal conditions needed to accomplish the photo-electrocoagulation-oxidation process. According to these study findings, when the combined method of photocatalyst-electrocoagulation-oxidation (Hp) was used, the highest removal efficiencies of nickel, cyanide, zinc, and copper were 85, 96, 94, and 98%, respectively. The results showed that using the combined photo-electrocoagulation-oxidation method increased the efficiency of simultaneous removal of pollutants by 10% compared to conventional electrocoagulation method. The reason for the increase in removal efficiency is the production of hydroxyl radicals simultaneously with the formation of coagulants produced by electrocoagulation process

Environmental Assessment of Heavy Metal Pollution in Freshwater Sediment, Serbia

The purpose of this study was to evaluate sediment heavy metals (Cd, Cu, Co, Mn, Cr, Ni, Pb and Zn) related to pollution in freshwater sediments in Serbia. The heavy metal enrichment determination in studied sediments was conducted by using total metal content with strong acidic digestion (HCl + HNO3 + HF), a calculated enrichment factor (EF), and application of correlation analysis and the box plot method. For identification of appropriate elemental normalisers for enrichment factor calculations, Fe, Al, Ti and Si were used. The significant variation in heavy metal distribution among samples collected in this large region, encompassing all Serbian watersheds, suggests the selective contamination of sediments by heavy metals. Values for EF indicate nil to moderate enrichment for most studied elements, except for Cd, Cu, and Zn at some sampling points, where the enrichment was, in some cases, even severe. The high content of heavy metals and EFs in Serbia is related to the human activities around the sampling sites. The results indicate that all elements used for normalisation in this paper can also be used to estimate the anthropogenic influence, with an exception of Co, which should be considered as an element for normalisation in future studies