Removal Rate Of Heavy Metals Research Articles

Bioremediation Technology Potential for Management of Soil and Water Pollution from Anticipated Rapid Industrialization and Planned Oil and Gas Sector in Uganda: A Review

Oil exploitation in many African countries is associated with litigation and conflicts to water and soil pollution. It is because of inadequate planning for management of oil spills and industrial effluents in environmentally sustainable manner. Uganda’s natural resources such as soils and water bodies are threatened by contamination due to rapid industrialization and rural-urban migration in established Industrial Business Parks and planned oil and gas production at Albertine Graben Region. The low level of compliance to industrial effluents discharge standards relevant to specific environmental receptors and activities within oil and gas sector development pose a big question of how to sustain the biodiversity and natural resource management. Experiences from elsewhere have shown bioremediation as a viable and proven option to provide potentially manageable solutions to resulting pollution as a substitute to modern well-known remediation methods, for it is relatively cheaper, more efficient and minimal toxic byproducts after treatment. The most used bioremediation agents in different studies reviewed are bacterial species especially Pseudomonas and Bacillus, followed by Aspergillus a fungi species, microalgae and aquatic plants such as duckweed, macrophytes and pteridophytes. Regardless of the waste produced in either oil and gas sector or industries, these agents have shown greater biodegradation rates. Pseudomonas sp. has a degradation efficiency of oil compounds ranging from 90% - 100%, and Aspergillus sp. 75% - 95%. Some aquatic plants can thrive in created wetlands with relatively still water such as Phragmites australis which can degrade hydrocarbons especially Aromatic compounds with benzene ring up to 95%. It can thrive in salty water with high pH range of 4.8 - 8.2. With industrial wastewater, algae is the most dominant with the degradation rates varying from 65% -100% and bacteria at 70% - 90%. Most of the reported results are in the developed country context. In developing countries, duckweed is reported as the commonest aquatic plant in wastewater treatment for removal of heavy metals because it is more tolerant to a wide range of environmental conditions and produce biomass faster. It has a removal rate of heavy metals between 90% and 100%. Basing on literature data analysis, bacteria are more suitable for treating water from oil pollution using Pseudomonas sp. Phragmites australis is suited for cleaning up oil in both water and soil. Duckweed is the best in treating water polluted with industrial effluents. This paper presents the different bioremediation methods that Uganda can potentially apply to mitigate the increased risk of environmental pollutions from planned industrialization and oil and gas development in the Albertine Graben Region.

Performance of Vetiver Grass (Vetiveria zizanioides) for Phytoremediation of Contaminated Water

In tolerance towards metal uptake, there is a need to evaluate the performance of vetiver grass for metal removal to reduce water impurity. This study was aimed to evaluate contaminant removal by vetiver grass at varying root length and plant density and determine the metal uptake in vetiver plant biomass. Pollutant uptake of vetiver grass was conducted in laboratory experiment and heavy metal analysis was done using acid digestion and Atomic Absorption Spectrometry. Findings indicated that the removal of heavy metal was decreased in seven days of the experiment where iron shows the highest percentage (96%; 0.42 ppm) of removal due to iron is highly required for growth of vetiver grass. Removal rate of heavy metals in water by vetiver grass is ranked in the order of Fe>Zn>Pb>Mn>Cu. Results also demonstrated greater removal of heavy metals (Cu, Fe, Mn, Pb, Zn) at greater root length and higher density of vetiver grass because it increased the surface area for metal absorption by plant root into vetiver plant from contaminated water. However, findings indicated that accumulation of heavy metals in plant biomass was higher in vetiver shoot than in root due to metal translocation from root to the shoot. Therefore, the findings have shown effective performance of vetiver grass for metal removal in the phytoremediation of contaminated water.

Removal of cadmium and zinc from contaminated wastewater using Rhodobacter sphaeroides.

Rhodobacter sphaeroides was used for bioremediation of wastewater polluted with cadmium (Cd) and zinc (Zn). The tolerance of the microorganism to selected heavy metals (HMs), as well as the effects of pH, temperature and inoculum size on the removal rate, was investigated. The remediation effects of R. sphaeroides were analysed at different initial concentrations of HMs. Bioremediation mechanisms were thoroughly discussed based on the results from the cell characterisation analysis. Cd and Zn could inhibit the growth of R. sphaeroides. However, Cd was more toxic than Zn, with corresponding EC50 values of 5.34 and 69.79 mg L-1. Temperature and pH had greater influence on the removal rate of HMs than inoculum size. The optimal conditions for temperature and pH were 35 °C-40 °C and pH 7, respectively. Initial concentration of HMs and remediation time also affected the removal rate. Rhodobacter sphaeroides had a relatively higher remediation effect under the present experimental conditions. The removal rates for Cd and Zn reached 97.92% and 97.76%, respectively. Results showed that biosorption and HM precipitation were the main bioremediation mechanisms. This information is necessary to better understand the removal mechanism of R. sphaeroides, and is significant for its pilot test and future practical application.

Phytoextraction of arsenic-contaminated soil with Pteris vittata in Henan Province, China: comprehensive evaluation of remediation efficiency correcting for atmospheric depositions.

Research on the appropriate method for evaluating phytoremediation efficiency is limited. A 2-year field experiment was conducted to investigate phytoremediation efficiency using the hyperaccumulator Pteris vittata on an arsenic (As)-contaminated site. The remediation efficiency was evaluated through the removal rate of As in soils and extraction rate of heavy metals in plants. After 2years of remediation, the concentration of total As in soils decreased from 16.27mgkg-1 in 2012 to 14.58mgkg-1 in 2014. The total remediation efficiency of As was 10.39% in terms of the removal rate of heavy metals calculated for soils, whereas the remediation efficiency calculated from As uptake by P. vittata was 16.09%. Such a discrepancy aroused further consideration on the potential input of As. A large amount of As was brought in by atmospheric emissions, which possibly biased the calculation of remediation efficiency. In fact, considering also the atmospheric depositions of As, the corrected removal rate of As from soil was 16.57%. Therefore, the results of this work suggest that (i) when evaluating the phytoextraction efficiency, the whole input and output cycle of the element of interest in the targeted ecosystem must be considered, and (ii) P. vittata has the potential to be used to remediate As-contaminated soils in Henan Province, China.

Adsorption Characteristics of Cd, Cu, Pb and Zn from Aqueous Solutions onto Reed Biochar

Carbon-based sorbents such as biochar and activated carbon have been proven to be cost-effective in removing pollutants containing heavy metals from wastewater. The aim of this study was using batch experiment to evaluate the adsorption characteristics of heavy metals in single-metal conditions onto reed biochar for treating wastewater containing heavy metals. The removal rates of heavy metals were in the order of Pb > Cu ≒ Cd ≒ Zn, showing the adsorption efficiency of Pb was higher than the other heavy metals. Freundlich and Langmuir adsorption isotherms were used to model the equilibrium adsorption data obtained from adsorption of Pb on reed biochar. For reed biochar, the Langmuir model provided a slightly better fit than the Freundlich model. Lead was observed on the biochar surface after adsorption by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The main functional groups of reed biochar were aromatic carbons. Overall, the results suggested that reed biochar could be useful adsorbent for treating wastewater containing Pb.

Use of flue gas desulfurization gypsum for leaching Cd and Pb in reclaimed tidal flat soil

A soil column leaching experiment was conducted to eliminate heavy metals from reclaimed tidal flat soil. Flue gas desulfurization (FGD) gypsum was used for leaching. The highest removal rates of Cd and Pb in the upper soil layers (0-30cm) were 52.7 and 30.5%, respectively. Most of the exchangeable and carbonate-bound Cd and Pb were removed. The optimum FGD gypsum application rate was 7.05kg·m(-2), and the optimum leaching water amount for the application was 217.74L·m(-2). The application of FGD gypsum (two times) and the extension of the leaching interval time to 20days increased the heavy metal removal rate in the upper soil layers. The heavy metals desorbed from the upper soil layers were re-adsorbed and fixed in the 30-70cm soil layers.

Electrokinetic Gathering and Removal of Heavy Metals from Sewage Sludge by Ethylenediamine Chelation

Wastewater sludge in Hangzhou Qige Municipal Sewage Plant was used to study the removal rate of heavy metals in sludge using a novel equipment designed in our laboratory. Five groups of sludge samples, mixed with ethylenediamine at the V/V ratio of 0, 0.04, 0.05, 0.06 and 0.07 (C2H8N2 /Sludge sample) were electrified for 120hours at a constant direct voltage of 18V. The effects of heavy metals removal on acidification of sludge generated by anode together with ethylenediamine chelation were studied. The results show that acidification generated by anode has played an important role in removing heavy metals from sludge. The addition of ethylenediamine has no significant effect on pH decrease and electric current density in the electric repair process; however, it effectively improved the removal of heavy metals in sludge. Moreover, it was found that various ethylenediamine dosage leads to different reaction efficiencies during the electrokinetic remediation. When ethylenediamine was added at a ratio of 0.06, the removal rates of Zn, Cu and Pb were 87.51%, 67.64% and 57.79% respectively, the overall removal rate is the best. The addition of ethylenediamine has a significant effect on the change of the migration process of heavy metals present in the experimental sludge. We observed the decreased amount of heavy metals in their stable species such as residual state and organic state as well as the increase in transferable form such as exchangeable state.

Heavy metal removal from MSS fly ash by thermal and chlorination treatments.

The thermal behavior of heavy metals in the co-incineration of municipal solid waste-sludge incinerator fly ash (MSS fly ash) was studied using a laboratory-scale tube furnace. The results indicate that without the addition of chlorinating agents, temperature was an important parameter and had significantly influenced on heavy metal removal, whereas the residence time had a weak effect. Between 900 and 1000 °C for 60 to 300 min, heavy metals reacted with chloride-inherent in the fly ash, and approximately 80 to 89% of Pb, 48% to 56% of Cd, 27% to 36% of Zn and 6% to 24% of Cu were removed. After the adding chlorinating agents, the evaporation rate of the heavy metals improved dramatically, where the evaporation rates of Cu and Zn were larger than that of Pb and Cd. As the amount of added chlorinating agents increased, the removal rate of heavy metals increased. However, the effect of the type of chlorinating agent on the chlorination of heavy metals differed considerably, where NaCl had the weakest effect on the removal rate of Cu, Cd and Zn. In terms of resource recovery and decontamination, MgCl2 and CaCl2 are the best choices due to their efficient removal of Zn.

Efficiency of Phragmites australis and Typha latifolia for heavy metal removal from wastewater

A cost-effective and promising technology has been demonstrated for the removal of copper (Cu), cadmium (Cd), chromium (Cr), nickel (Ni), iron (Fe), lead (Pb) and zinc (Zn) from urban sewage mixed with industrial effluents within 14 days. With the help of P. australis and T. latifolia grown alone and in combination batch experiments were designed to assess the removal of heavy metals from the wastewater collected from 5 sampling stations. The results revealed that P. australis performed better than T. latifolia for Cu, Cd, Cr, Ni, Fe, Pb and Zn removal, while mixing of the plant species further enhanced the removal of Cu to 78.0±1.2%, Cd to 60.0±1.2%, Cr to 68.1±0.4%, Ni to 73.8±0.6%, Fe to 80.1±0.3%, Pb to 61.0±1.2% and Zn to 61.0±1.2% for wastewater samples from Raj Ghat. Negative correlation coefficients of Cu, Cd, Cr, Ni, Fe, Pb and Zn concentrations in wastewater with the retention time revealed that there was an increase in the heavy metal removal rate with retention time. P. australis showed higher accumulative capacities for Cu, Cd, Cr, Ni and Fe than T. latifolia. P. australis and T. latifolia grown in combination can be used for the removal of Cu, Cd, Cr, Ni, Fe, Pb and Zn from the urban sewage mixed with industrial effluents within 14 days.

PCR-DGGE and real-time PCR dsrB-based study of the impact of heavy metals on the diversity and abundance of sulfate-reducing bacteria

Sulfate-reducing bacteria (SRB) are widely used for heavy metal (HM) treatment in bioreactors but their growth and biological activity can be inhibited by such treatment. Here, bioreactor experiments were used to investigate changes in the SRB community and the copy number of the dissimilatory sulfite reductase β-subunit functional gene (dsrB) under high doses of sulfates and HMs. The SRB community was investigated using polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) and sequencing techniques, while the dsrB gene abundance was measured by quantitative real-time PCR (qRT-PCR). The sulfate reduction rate was initially much higher in reactors without HMs than in those containing HMs (p = 0.001). Sulfate levels were reduced by 50% within the first 3 days of operation. As a result, the HM removal rate was initially much lower in the reactors containing HMs. Most of the HMs reduced to safe limits within 9 ~ 12 days of operation. The SRB community mainly consisted of Desulfovibrio vulgaris, D. termitidis, D. desulfuricans, D. simplex and Desulfomicrobium baculatum, as determined by PCR-DGGE. qRT-PCR revealed a decreasing trend in the copy numbers of a functional gene (dsrB) after 6 days in samples lacking HMs; however, the opposite trend was observed in the HM-containing samples.

Removal of Heavy Metal Elements and Nutrients by <I>Pontederia cordata</I> and <I>Phragmites australis</I> Constructed Wetlands

For studying the potential applications of Pontederia cordata L.as a constructed wetland plant,the removal effects of P.cordata and Phragmites australis Trin.ex Steud.on nutrients and heavy metal elements in the wetlands were compared.Mono-cultivated small-scale wetlands were constructed using pots(80 cm-50 cm-45 cm,the upper diameter-bottom diameter-high).The results showed that the removal rates for TN and BOD5 by P.cordata was significantly higher than those by P.australis(P 0.05).But there was no significant difference between them for the removal of Cd2 + and Pb2+.Content distribution of Cd2+and Pb2+ in both plants was as follows: root stem leaf.For both the wetlands,there was little difference in nutrient removal between hydraulic retention time(HRT) of 2 d and 7 d,but heavy metal removal rate at HRT of 7 d was significantly higher than that at HRT of 2 d,indicating that the removal of heavy metals was slower than that of nutrients in the constructed wetlands.These results suggest that P.cordata has a good application potential in constructed wetlands because of its good visual effects and high removal rates for wastewater pollutants.

Effects of Different Thiobacillus on Bioleaching of Heavy Metals of Sewage Sludge in a Sequencing Batch Reactor

A bioleaching experiment was carried out in two sequencing batch reactors (SBR) of 80 L. Acidithiobacillus thiooxidans (A. t) and Acidithiobacillus ferrooxidans (A. f) were enrichment cultured by adding sulfur powder and ferrous sulfate as substrate respectively. Sequential batch leaching ran for three periods in succession. The average removal rate of As, Cd, Cr, Cu, Ni, Pb, Zn was 90.46%, 90.28%, 90.70% and 79.70%, 81.19%, 84.52% respectively. The average loss rate of total nutrient (total account of organic matter, TN, TP and TK) is 35.36%, 33.36% and 35.54% for three runs in sequence. Comparing with A. f, the acidification time of A. t is shortened by 3.0, 6.6 and 4.9 d, with the increase of 13.5 %, 11.2% and 7.3% for the removal rate of heavy metals.

Characterization of sludge generated by electrocoagulation for the removal of heavy metals

In this work, heavy metal removal by electrocoagulation (EC) was evaluated, and the characteristics of the EC sludge were investigated to understand the behavior of heavy metals during EC. It was found that iron electrodes are superior to aluminum due to the negatively charged surface. Using iron electrodes, the removal rate of heavy metals increased as the current density increased and as the total initial heavy metal amount, either single or multiple heavy metals, decreased, suggesting that the efficiency is closely related to the floc amount. The X-ray diffraction (XRD) patterns showed that the chemical species in the EC sludge are different from those obtained by chemical equilibrium analysis, indicating that many electrochemical and chemical reactions occur during EC. The pH variation during EC and the XRD patterns of the sludge indicate that precipitation, adsorption, and chemical oxidation/reduction in the vicinity of the electrodes contribute much to Pb(II), Cd(II), and Cu(II) removal, respectively. In addition, the formation of Pb(OH)Cl, β-Cd2(OH)3Cl, and CuCl was found, indicating that chloride from the background electrolyte contributes to heavy metal precipitation. Scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy analysis also showed that Pb(II) and Cu(II) are encapsulated by the flocs.

Removal of iron, chromium and lead from waste water by horizontal subsurface flow constructed wetlands

AbstractBackgroundTwo pilot scale horizontal subsurface flow constructed wetlands (HSFCWs), with a planted area of 15 m2 each, were constructed in Puglia, Italy, and planted with hydrophytes (Phragmites australis and Typha latifolia), while a similar field of equal size was used as a control. The primary aim of the present work was to assess the removal of three heavy metals from waste water, in relation to the evapotranspiration, using HSFCWs.ResultsResidence time distributions in both planted HSFCWs indicated that the Typha field had porosity of 0.16 and exhibited more ideal plug flow behavior (Pe = 29.7), compared with the Phragmites field (Pe = 26.7), which had similar porosity. The measured hydraulic residence times in the planted fields were 35.8 and 36.7 h, for Typha and Phragmites, respectively, at waste water flow rates of 1 m3 d−1 (corresponding to hydraulic loading rate of 66.7 mm d−1). Heavy metals concentrations at the inlet were 2 mg/L, for each heavy metal, while at the outlet of the fields were Cr = 0.23 mg L−1, Pb = 0.21 mg L−1 and Fe = 0.18 mg L−1 in the Phragmites field, and the removal rates were 87, 88 and 92% of Cr, Pb and Fe, respectively. The Typha field showed a similar behavior with concentrations equal to Cr = 0.19 mg L−1, Pb = 0.23 mg L−1 and Fe = 0.16 mg L−1 and removal percentages of 90, 87, and 95% of Cr, Pb and Fe, respectively. The control field showed metal removals slightly lower (86, 78 and 88% for Cr, Pb and Fe, respectively).ConclusionsHSFCWs are appropriate for removing heavy metals from waste water. Evapotranspiration may significantly reduce the amount of discharged flow and may influence the removal rate of heavy metals. © 2013 Society of Chemical Industry

참깨 부산물 Biochar의 중금속 흡착특성

참깨 부산물의 중금속 흡착제로서 가능성을 검토하기 위해 <TEX>$600^{\circ}C$</TEX>에서 1시간동안 열분해 한 참깨 부산물 biochar를 이용하여 중금속 오염폐수 중의 중금속 흡착특성을 조사하였다. Biochar의 중금속 제거효율은 Pb>Cu>Cd>Zn 순으로 Pb의 흡착효율이 가장 높게 나타났다. 참깨 부산물 biochar를 이용한 흡착실험 결과를 Freundlich와 Langmuir 등온흡 착식에 적용하여 각각의 중금속 인자를 산출한 결과 Langmuir와 Freundlich 등온흡착식 모두에서 Pb의 흡착능력이 Cu, Cd 및 Zn에 비해서 우수한 것으로 나타났다. Pb의 경우는 Langmuir 등온흡착식이 Freundlich 등온흡착식에 비해 더 적합하였으나 Cu, Cd 및 Zn의 경우 저농도에서 약간 차이는 있었으나 두 등온흡착식 모두 적합하였다. 전자현미경 (SEM)을 이용하여 중금속 흡착 전 후의 biochar 표면을 관찰한 결과 중금속 흡착 후에 각각의 중금속이 흡착되어 있는 것을 관찰 할 수 있었다. FT-IR 분석결과 중금속은 주로 방향족 C=O ring stretching (<TEX>$1160cm^{-1}$</TEX> <TEX>$1384cm^{-1}$</TEX> 및 <TEX>$1621cm^{-1}$</TEX>)에서 흡착되는 것으로 관찰되었다. 이상의 결과를 미루어 볼 때 참깨 부산물로 제조한 biochar는 중금속 흡착제로서의 활용 가능성이 높을 것으로 판단된다. Little research has been conducted to explore the heavy metal removal potential of biochar. The adsorption characteristics of heavy metals by sesame waste biochar (pyrolysis at <TEX>$600^{\circ}C$</TEX> for 1 hour) as heavy metal absorbent were investigated. The sesame waste biochar was characterized by SEM-EDS and FT-IR, and heavy metal removal was studied using Freundlich and Langmuir equations. The removal rates of heavy metals were higher in the order of Pb>Cu>Cd>Zn, showing that the adsorption efficiency of Pb was higher than those of any other heavy metals. Freundlich and Langmuir adsorption isotherms were used to model the equilibrium adsorption data obtained for adsorption of heavy metals on biochar produced from sesame waste. Pb, Cu, Cd and Zn equilibrium adsorption data were fitted well to the two models, but Pb gave a better fit to Langmuir model. Heavy metals were observed on the biochar surface after adsorption by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Main functional groups were aromatic C=O ring (at <TEX>$1160cm^{-1}$</TEX>, <TEX>$1384cm^{-1}$</TEX> and <TEX>$1621cm^{-1}$</TEX>) by FT-IR analysis. Thus, biochar produced from sesame waste could be useful adsorbent for treating heavy metal wastewaters.

Assessing the resistance and bioremediation ability of selected bacterial and protozoan species to heavy metals in metal-rich industrial wastewater

BackgroundHeavy-metals exert considerable stress on the environment worldwide. This study assessed the resistance to and bioremediation of heavy-metals by selected protozoan and bacterial species in highly polluted industrial-wastewater. Specific variables (i.e. chemical oxygen demand, pH, dissolved oxygen) and the growth/die-off-rates of test organisms were measured using standard methods. Heavy-metal removals were determined in biomass and supernatant by the Inductively Couple Plasma Optical Emission Spectrometer. A parallel experiment was performed with dead microbial cells to assess the biosorption ability of test isolates.ResultsThe results revealed that the industrial-wastewater samples were highly polluted with heavy-metal concentrations exceeding by far the maximum limits (in mg/l) of 0.05-Co, 0.2-Ni, 0.1-Mn, 0.1-V, 0.01-Pb, 0.01-Cu, 0.1-Zn and 0.005-Cd, prescribed by the UN-FAO. Industrial-wastewater had no major effects on Pseudomonas putida, Bacillus licheniformis and Peranema sp. (growth rates up to 1.81, 1.45 and 1.43 d-1, respectively) compared to other test isolates. This was also revealed with significant COD increases (p < 0.05) in culture media inoculated with living bacterial isolates (over 100%) compared to protozoan isolates (up to 24% increase). Living Pseudomonas putida demonstrated the highest removal rates of heavy metals (Co-71%, Ni-51%, Mn-45%, V-83%, Pb-96%, Ti-100% and Cu-49%) followed by Bacillus licheniformis (Al-23% and Zn-53%) and Peranema sp. (Cd-42%). None of the dead cells were able to remove more than 25% of the heavy metals. Bacterial isolates contained the genes copC, chrB, cnrA3 and nccA encoding the resistance to Cu, Cr, Co-Ni and Cd-Ni-Co, respectively. Protozoan isolates contained only the genes encoding Cu and Cr resistance (copC and chrB genes). Peranema sp. was the only protozoan isolate which had an additional resistant gene cnrA3 encoding Co-Ni resistance.ConclusionSignificant differences (p < 0.05) observed between dead and living microbial cells for metal-removal and the presence of certain metal-resistant genes indicated that the selected microbial isolates used both passive (biosorptive) and active (bioaccumulation) mechanisms to remove heavy metals from industrial wastewater. This study advocates the use of Peranema sp. as a potential candidate for the bioremediation of heavy-metals in wastewater treatment, in addition to Pseudomonas putida and Bacillus licheniformis.

Quick Start Study on Bioleaching Method

The experiment uses the Shenyang northern sewage treatment plant two sink the pond sludge was the indigenous Thiobacillus enrichment culture, through the matrix of different proportion, to find the most suitable matrix proportion, so as to shorten the bioleaching process start time, improve the bioleaching process for heavy metal removal efficiency. By usihng the method developed by mixing S bacteria predominantly mixed bacteria liquid, will raise the mixed strain cycle was shortened to 11 days, the best ratio of S, Fe2+ matrix is determined as 3 : 1, the matrix culture mixed Thiobacillus is faster, and can greatly improve the bioleaching boot efficiency. Fe2+ dosing is able to activate the bacterial Fe2+ enzyme synthesis, be helpful for accelerating thiobacilli on s oxidation using elemental sulfur, while also promoting microorganism to use Fe2+. Using the technology of biological leaching experiment on heavy metal removal rate is higher, compared with a single strain has more engineering application and popularization value.

적니와 석회석을 이용한 혼합 중금속(Cr6+,Cu2+,As3+,Pb2+)의 제거

This study examined the removal rate of heavy metals from synthetic control water using red mud and lime stone. Overall, the percent of absorption obtained in this study for the red mud treatment was 94.0% (), 67.1% (), 37.5% (), and 36.6% (), while that of lime stone was (30.8%), (16.5%), (11.5%), and (8.9%). The kinetic data presented that the slow course of adsorption follows the Pseudo first and second order models, the equilibriuim adsorption of and obeys Freundlich isotherm model, while the adsorption of obeys only Langmuir model. The results also showed that adsorption rate slightly increased with increasing pH from 5 to 9. Interestingly, this trend is similar to results obtained as function of loading amount of red mud. Meanwhile, an unit adsorption rate was slightly decreased. For lime stone, it did not much change in adsorption as function of treatment amount. Consequently, it was concluded that the absorbents can be successfully used the removal of the heavy metals from the aqueous solutions.

Linear and Nonlinear Modeling for Predicting Nickel Removal from Aqueous Solutions

Mathematical models are widely used to predict removal rates of heavy metals from aqueous solutions. In this study, partial least squares (PLS), wavelet neural network (WNN), and support vector regression (SVR) were used to predict the amount of nickel (Ni) removal by dried sunflower stalks from a synthetic wastewater, based on experimental data sets from a laboratory batch mode. Effect of pH, initial concentration of the adsorbate, contact time, and dose of the adsorbent was considered in the adsorption process. Results showed that the coefficient of determination (R2 or q2) for the relationship between the model-predicted and experimental data of the final concentration of Ni at calibration stage was 0.87, 0.98, and 0.99 and for cross-validation was 0.73, 0.8, and 0.91 for PLS, WNN, and SVR models, respectively. It was concluded that the SVR model performed relatively better than the other models due to its capability in capturing the nonlinear relationships between the variables. Grid search was a fast and effective method that optimized the hyperparameters in SVR modeling. The SVR and WNN models were also used to investigate the effect of different variables on Ni removal efficiency. The results showed that initial concentration of Ni and pH of the solution were more important in the adsorption process, relative to contact time and dose of the adsorbent.

Experimental Research for Heavy Metal Lead and Zinc Smelting Wastewater by Electroflocculation

In this paper,author use electroflocculationt to deal with heavy metal lead and zinc smelting wastewater,disiscussing the impact of electroflocculation to heavy metal removal rate under different pH,electrolytic voltage,electrolysis time ,plate spacing conditions. The results show that: heavy metal removal rate achieve the best effects when the situationgs is that pH is 11, electrolysis voltage is 2v, electrolysis time is 30 min , plate spacing is 1.2cm.Cd removal efficiency is 100% ,99.92 % removal efficiency of Zn,95.53% removal efficiency of Pb and 98.64% removal efficiency of Cu