Development of a Precipitation Based Separation Scheme for Selective Removal and Recovery of Heavy Metals from Cadmium Rich Electroplating Industry Effluents

Abstract

The treatment of electroplating wastes is a serious worldwide problem, because of their high content of many different heavy metals. Chemical precipitation based treatment methods could be an important alternative for fractional selective separation of heavy metals if they are systematically developed by sequencing of pH, adjusting the added portions of precipitating agents, and selecting the optimum time period before removing the precipitate from the solution. In this study, for selective removal and recovery of Cd from real electroplating bath wastewater (containing high amounts of Cd, medium amounts of Zn, Cu, Fe and small amounts of Ni, Co, Mn), a precipitation based separation scheme was developed. The scheme comprised of three consecutive steps: 1) Acid treatment with nitric acid (HNO₃). Cyano‐metal complexes were decomposed in acidification step and complete removal of iron was achieved. 2) Alkali precipitation by sodium hydroxide (NaOH). Large portion of Cd was recovered as pure Cd(OH)₂. 3) As a polishing step sulfide precipitation by sodium sulfide (Na₂S) was applied. pH was the critical parameter in sulfide precipitation. Addition of sodium sulfide in alkali pH range led to cadmium precipitation whereas copper was totally precipitated in acidic pH range. The sulfide precipitation step may be replaced by more environmentally friendly steps (e.g. polymer enhanced ultrafiltration) until the heavy metal concentrations were reduced down to suitable discharge limits.     

Bioleaching of heavy metals from dewatered sludge by Acidithiobacillus ferrooxidans

The feasibility of bioleaching for removal of heavy metals from dewatered sewage sludge using an iron‐oxidizing bacterium Acidithiobacillus ferrooxidans was investigated. The influence of seven process parameters including cell adaptation, total amount and particle size of the sludge, initial concentrations of Fe²⁺ and At ferrooxidans, and addition of inorganic nutrients and sulfur were evaluated in terms of the solubilization of Zn, Cu and Cr. When sludge‐adapted cells, addition of inorganic nutrients and lower sludge content were involved, higher yields of metal extraction were obtained. However, higher initial concentrations of At ferrooxidans and Fe²⁺, fine particle size of the sludge and S addition did not improve the metals' solubilization during an experimental period of 7 days. As a result of a long‐term (40 days) bioleaching experiment, 42% of Zn (1300–1648 mg kg^?1), 39% of Cu (613–774 mg kg^?1) and 10% of Cr (37–44 mg kg^?1) in the sludge were leached into the solution. The results indicate that a bioleaching process conducted under operationally optimal conditions can be effectively employed for the removal of heavy metals from sewage sludge before land application. Copyright © 2005 Society of Chemical Industry     

Benefits and risks of using a combination of sewage sludge and chemical fertilizer on rice in acid sulfate soil

Field experiments were conducted in acid sulfate soils in the CentralPlain of Thailand to study a combination of sewage sludge and urea as nitrogensources for rice. Rice yield, nitrogen mineralization, heavy metal availableanduptake were quantified. The experiment design was a split plot in 2×4 factorialdesign. Two rates of nitrogen (75 and 150 kg Nha^–1) were assigned to main plots and four combinationsof urea and sewage sludge as source of N to subplots. The four combinationswerein % of N from urea (U) and from sewage sludge (S), as follows: 33% N from U + 67%N from S, 67% N from U + 33% N from S, 100% N from U + 0% N from S, and 0% N fromU + 100% N from S. Nitrogen mineralization in these treatments was tested in bothopen and closed systems to study N balance at different growth stages of rice.The results showed that nitrogen at 75 kg N ha^–1 gavea better grain yield than at 150 kg N ha^–1 and control(0 kg N ha^–1). At the higher nitrogen applicationrate, an increase in the biomass with reduced grain yield was observed. Amongthe sources of N, the combination of urea 33% N and sewage sludge 67% Nresultedin highest grain yield. Nitrogen mineralization of sewage sludge in acidsulfatesoil was low. Nitrogen mineralization from urea and urea combination withsludgetreatment were greater than sewage sludge application alone. Due to lowextractable heavy metals in sewage sludge applied soil, the heavy metal contentin milled grain and straw were below allowable limits set by US standards.Results indicated that a combination of urea and quality sewage sludge could beused as a fertilizer nitrogen source for rice, without risks associated withtoxic heavy metals.     

城市污泥中重金属去除技术研究

重金属污染是目前城市污水处理厂污泥农用的主要障碍之一。综述了城市污泥中重金属去除的常用四种技术：化学浸提、生物淋滤、动电技术和固化-稳定化,同时分析了污泥中重金属去除技术的发展方向。     

Removal of lead,cadmium and zinc from aqueous solutions by precipitation with sodium Di‐(n‐octyl) phosphinate

Sodium di‐(n‐octyl) phosphinate (NaL) was used as a precipitating agent to remove heavy metals from aqueous nitrate solutions. Cadmium, zinc and mixtures of lead, cadmium and zinc were precipitated in the form of PbL_2(s), CdL_2(s), and ZnL_2(s). Lowering the pH of the feed solution reduced the removal of the metals as some of the phosphinate precipitated in the acid form as HL_(S). The removal of lead, cadmium, and zinc, from a solution containing the three metals gave a selectivity in the order Zn > Pb > Cd. Predictions of an equilibrium‐constant model, using measured solubility products of the precipitates and literature values of stability constants, gave metal removals, loss of precipitating agent, and equilibrium pH in good agreement with measured values.     

Procéadéa de solubilisation biologique des méataux dans les boues anaéarobies d'éapuration: Filtrabilitéa,neutralisation et teneurs en n et p des boues traitéaes

Biological solubilization of heavy metals in anaerobic sewage sludge was performed in a continuous reactor with two mean hydraulic residence times (0.5, 0.75 day). Following filtration of the processed sludge, the amount of solubilized Cu and Zn decreased from 92% and 94% to 78% and 77% respectively in the sludge. Most iron reprecipitates in filtered sludge. Processed sludge is easy to deshydrate. The filtrability index (r_0.5) of processed sludge is 38 times smaller than anaerobic sludge, without adding polymers. It was found that the values obtained for r_0.5 and inferior to 8 × 10¹² m/kg enable the sludge to be dehydrated in a plate filter press without adding polymers. Centrifugation can also be used. The content in nitrogen, phosphorus and hydrolysable phosphorus remain unchanged during processing. 47% of the ammonia is lost in the filtrate. The neutralization of processed sludge (pH = 7) and contaminated supernatant (pH = 10) require a small quantity of base. The selective precipitation of metals could allow the recovery of Cu in the generated metallic sludge. Finally, results show the preliminary feasability of the process. A pilot scale study could enable the scale-up of the process.     

Investigations on twenty Australian sewage sludges — their evaluation by means of chemical analysis

To evaluate twenty sludges from different places in Australia for disposal on arable land, these sludges were extracted with (a) HNO₃ to determine the ‘total’ contents of some heavy metals and other elements; (b) a solution containing DTPA to determine contents of ‘available’ heavy metals; and (c) with a CaCl₂-solution to determine contents of water-soluble heavy metals and some other elements. Measurements of the pH of the sludges, their electrolytic conductivity, NaHCO₃-extractable P, water-extractable Cl, and contents of ash and organic carbon were also made. The HNO₃-extractable Cd, Cu, Mn, Ni, Pb, and Zn in the sludges were compared with those in sludges from three other countries. High correlations between HNO₃-extractable and DTPA-extractable metals were found in the Australian sludges; therefore, the HNO₃ is equally good as the DTPA as an extractant of heavy metals in sewage sludges. The correlations between HNO₃- and CaCl₂-extractable Cd, Cu, Mn, and Zn were not significant. ‘Young’ and ‘aged’ sludges from the same treatment plants consistently differed in their Na and Cl contents, which were lower in the ‘aged’ sludges. A wheat experiment treated with high application rates of a saline and metalliferous sludge showed that the balance of nutrients and the amount of soluble salts in a sewage sludge are of greater direct importance to the growth of plants than the heavy metal content of that sludge.     

城镇污水处理厂污泥中重金属去除方法研究进展

城镇污水处理厂污泥中的重金属是污泥资源化利用的潜在危害之一,因此如何有效去除污泥中的重金属是当前亟待解决的问题。在分析我国污泥重金属含量现状的基础上,对动电技术、生物沥滤法、化学浸提法和植物提取法等重金属去除方法进行了比较。通过比较可知,这四种方法的主要优势分别为去除效率高、适用范围广、操作简单、费用低廉。在分析这些技术与方法各自特点的基础上,指出了这些去除方法各自存在的问题及其研究进展。     

Organic reagents for removing heavy metals from a 10-34-0 (N-P2O5-K2O) grade fertilizer solution and wet-process phosphoric acid

Fertilizer solutions and wet-process phosphoric acid (WPA) contain heavy metal impurities such as cadmium, zinc, lead, copper, manganese, and chromium. Trisodium trithiocyanuric acid (TMT-15), sodium trithiocarbonate (5% Na₂CS₃), and sodium polythiocarbonate (Thio-Red II) were evaluated as precipitating agents for heavy metals in a 10-34-0 (N-P₂O₅-K₂O) grade fertilizer solution and WPA. A water-insoluble starch xanthate was also evaluated as an adsorbent for the heavy metals in 10-34-0 (N-P₂O₅-K₂O) and WPA. Arsenic (24–99+%), cadmium (36–97+%), copper (98+%), mercury (96+%), lead (83–88+%), and zinc (8–83+%) precipitated from 10-34-0 (N-P₂O₅-K₂O) upon the addition of each organic reagent, while levels of manganese and chromium were unaffected. Mercury (97+%), lead (75+%), cadmium (11–38%), copper (99+%), and chromium (3–35%) precipitated from WPA upon the addition of 5% Na₂CS₃ and Thio-Red II, while precipitation of manganese and zinc was negligible. The water-insoluble starch xanthate adsorbed mercury (96+%), copper (38–98+%), and lead (24–75%) from 10-34-0 (N-P₂O₅-K₂O) and WPA while adsorption of arsenic, cadmium, manganese, chromium, and zinc was negligible.     

城市污泥重金属电动修复技术与应用研究进展

重金属污染是目前城市污水处理厂污泥农用的主要障碍之一。电动修复作为一门新兴的污染环境介质绿色修复技术,具有投资少、去除效率高和处理时间短等优点。特别是对于水力渗透性差的污泥,电动修复技术具有良好的应用前景。论文介绍了城市污泥重金属电动去除技术原理,并综述了近几年国内外在修复效果及其影响因素等方面的研究现状。同时,对该技术应用过程中存在的问题和未来研究方向进行了讨论和展望。     

Effects of phosphorus-rich sawdust biochar sorption on heavy metals

ABSTRACT

The aim of this paper is to study the efficiency of typical heavy metals in electroplating sludge in terms of different phosphorus dosages (0.5 wt.%, 1 wt.% and 3 wt.%), initial pH (2, 3, 4, 5 and 6) and adsorption times (1, 3, 5, 7 and 12 h) of biochar. The heavy metal speciation was determined after adsorption to estimate the stability of ion-adsorption precipitation. Results show that phosphorus-modified biochar enhances the removal efficiency of heavy metals. Low mobility of heavy metal speciation was investigated. It is also shown that initial pH has a significant impact on the heavy metal speciation after adsorption.     

Solidification of electroplating sludge using alkali-activated pulverized fuel ash as cementitious binder

This work investigated the potential for utilization of alkali-activated PFA as solidification binder to treat electroplating sludge. The sludge was solidified using 30 wt.% of lime and 70 wt.% of PFA. Two alkali activators, Na₂SiO₃ and Na₂CO₃, were added at 0, 4, 6, and 8 wt.%. Results showed that early strength development of lime-PFA cements with Na₂SiO₃ and Na₂CO₃ was considerably higher than those without. Addition of electroplating sludge resulted in reduced strength. The strength reduction was greater when 4% Na₂SiO₃ activator was used than when 8% Na₂CO₃ activator was used. A higher pH of Na₂SiO₃ solution (pH=13.5) compared to that of Na₂CO₃ solution (pH=11.9) resulted in resolubilization of metal hydroxides from the electroplating sludge, which competed with calcium ion for soluble silicate. In addition, Pb, Cd, and Cu were not found in the toxicity characteristic leaching procedure (TCLP) leachates. Cr, Zn, and Fe were detected and in some cases Cr exceeded U.S. EPA allowable limits.     

污泥中重金属去除的技术

介绍了污泥中重金属存在的形态,综述了污泥中重金属去除的常用的四种技术化学浸出、生物浸出、电分离和超临界流体萃取,重点介绍了化学浸取技术的原理和特点,并对诸项技术的优点以及存在的问题进行了评述。     

Pilot plant investigation on petrochemical wastewater treatmentfor the removal of copper and chromium with the objective of reuse

There has been great demand for development of technologies that remove toxic heavy metal ions from wastewater. Chemical precipitation operation is known to remove heavy metal ions from water. In this study applicability of alkaline reagents such as Ca(OH)₂ (lime) and NaOH (caustic soda) in removing copper and chromium ions were evaluated. Separation of heavy metals such as chromium compounds from petrochemical industries' cooling water wastes was achieved by conversion of hexavalent chromium, Cr(VI), to trivalent chromium, Cr(III). Maximum conversion occurred in the pH range of 2.0 and 2.3, adjusted by ferrous sulfate and sulfuric acid. Maximum precipitation of Cr(III) occurred at pH 8.7 with addition of Ca(OH)₂, followed by mixing and 2-h sedimentation. At the end, the concentration of chromate was reduced from 30 ppm to 0.01 ppm. In the case of copper, which is found in the form of cupro-ammonia in ammonia plant wastes, it was observed that the presence of ammonia in wastewater prevents effective chemical precipitation. Therefore, the quantity of ammonia was reduced by aeration. The optimum aeration rate was determined to be 70 L/min, and it was found that ammonia concentration reached equilibrium after 5.0 h o f aeration. Furthermore, hydroxide and carbonate methods were evaluated with respect to precipitation of heavy metals at bench scale, and the former was selected as the method of choice. The results obtained in the Jar test were then applied to pilot scale, and it was determined that the optimum pH for maximum copper precipitation was about 12.0 for both lime and caustic soda used in the hydroxide precipitation method. Lime was preferred due to economics and its high speed of precipitation. Finally, using established methods described here, the concentration of copper followed by coagulation with lime, mixing, 2-h sedimentation and filtration through Whatman 0.45 Am filters was reduced from 48.51 mg/L to 0.694 mg/L, which is below the environmental standards for water resources.     

SELECTIVE RECOVERY OF COAGULANTS FROM WATER CLARIFIER SLUDGE BY THE USE OF FIBROUS ION EXCHANGERS

ABSTRACT

A new technology for removal and recovery of coagulants from water clarifier sludge has been optimized at laboratory scale pilot plant level. The process is based on the use fibrous exchangers showing good kinetic and thermodynamic performance toward coagulant species (Al, Fe) present in the acidic leachate (pH 3.5) from water clarifier sludge. The innovation allows for the solution of the environmental problem related to clarifier sludge disposal (residual solids after metals leaching are safely applied to land), and quantitative recovery of coagulants to the water potabilisation operations

Process optimisation, by using real clarifier sludge from the Sinni River Water Works (Apulian Water Authority, S.E. Italy), was carried-out and results are illustrated in the paper. A commercial weak cation fibrous exchanger (Fiban K4) with carboxylate functionality, selectively removed aluminium and ferric species in “moving bed” unit operations with the resin re-circulating through the stationary exhaustion and regeneration baths. Resin regeneration was efficiently carried-out by the use of 0.4M NaOH solution for quantitative recovery of almost pure coagulants, ready for reuse. Together with process optimisation, the paper also reports some mechanistic indications on the fibrous resin performance toward polyvalent metal species retention at the resin functional groups.     

Conditioning and Dewatering of Phosphorus-Rich Biological Sludge

The conditioning and dewatering of phosphorus-rich biological sludge, obtained from a pilot-scale biological phosphorus removal plant, was investigated. Dual conditioning utilizing a polyampholyte (AC4601) in combination with aluminum chloride (AlCl₃), ferric chloride (FeCl₃), and calcium chloride (CaCl₂) was studied. Capillary suction time (CST) and specific resistance to filtration (SRF) were utilized to assess sludge dewaterability. The dewaterability and removal of dissolved phosphorus from the phosphorus-rich sludge were examined. Compared with conditioning with only AC 4601, dual conditioning by adding 49 kg/ton of AlCl₃ prior to addition of AC4601 resulted in formation of large flocs, better dewaterability, and removal of 50% of soluble phosphorus. Better dewaterability, even larger flocs (> 1 cm), and 75% removal of soluble phosphorus were found when dosage of AlCl₃ increased to 189.2 kg/ton. The use of alumina (Al₂O₃) in combination with AC4601 could achieve equivalent dewaterability. However, only insignificant removal of soluble phosphorus (ca. 10%) was found. Sludge conditioning utilizing FeCl₃ and AC4601 was also very effective. A higher dosage of AC4601 was required and insignificant removal of soluble phosphorus was found when CaCl₂ was used in combination with AC4601. The interactions between hydrolyzed species of trivalent metal ions and polyampholyte contributed to enhanced dewaterability. Precipitates acted as skeleton builder and assisted in dewaterability as well. In addition, the removal of phosphorus was due to its precipitation reactions with metal ions. This study demonstrated an alternative way to condition phosphorus-rich sludge that could control the release of phosphorus from sludge to aqueous phase under anaerobic environment and achieve enhanced dewaterability simultaneously.     

螯合剂处理重金属污染底泥的实验研究

引言 底泥是各种来源的营养物质进入水体后,经沉淀、吸附、生物吸收等多种途径最终沉积于水体底部,形成疏松状、富含有机质和营养盐的灰黑色淤泥.因此沉积物曾一度被看作是水体环境各种污染物质的最终储存场所.底泥中含有丰富的有机质、腐殖质,是一种良好的有机肥料[1-2],因此,土地利用是底泥资源化处置利用的重要方式.英、法等发达国家疏浚底泥的农用率高,而我国利用率相当低[3].     

Crossflow Surfactant-Based Ultrafiltration of Heavy Metals from Waste Streams

Abstract

Five heavy metals (cadmium, lead, copper, nickel, and zinc) in a simulated wastewater, alone and together, were substantially removed by surfactant-based ultrafiltration using natural surfactants such as a derivative of cholesterol (deoxycholic acid) and lecithins. Selective and total removal of metal ions has been achieved by applying an appropriate level of surfactant-to-metal ratio (S/M). The underlying principle is to increase the size of the target metal ions by fixing them to larger surfactant macromolecules so they can be retained by a compatible membrane. Deoxycholic acid exhibited more efficiency in metal removal than did lecithin and sodium dodecyl sulfate. This research showed that transmembrane pressure had a minimal effect on metal removal whereas S/M had a substantial influence. The optimal S/M for considerable metal removal (99.9 + rejection ratio) is around 2.5 and 5 for deoxycholic acid and sodium dodecyl sulfate, respectively. The binding of metals to surfactant in the absence of membrane interferences was also determined by a centrifuge method.     

Characterization and treatment of wastewater produced during the hydro-metallurgical extraction of germanium from fly ash

The present work dealt with the characterization and treatment of liquid wastes produced during the hydrometallurgical recovery of germanium (Ge) from fly ash. The main metals causing reasons for environmental concern were arsenic (As), nickel (Ni) and antimony (Sb). Precipitation using calcium hydroxide (hydrated lime) was the most efficient method for treating wastewaters with high levels of As, Sb and Ni (up to 99.9% removal). However, relatively large quantities of sludge were produced due to the large doses employed. Reverse osmosis (RO) also proved to be an efficient method achieving heavy metal removals of over 90%. Large quantities of concentrate were produced which required subsequent treatment by lime precipitation. A combined treatment of RO and lime precipitation of the resultant concentrate stream yielded a 97.5% removal of metals. At the same time, a stream with a concentrated level of catechol was obtained that could be reused in the extraction of Ge.     

Copper (2+), Zinc (2+), and Nickel (2+) Uptake by Activated Sludge

Abstract

This paper reports the results obtained on copper, zinc, and nickel uptake by activated sludge in a completely mixed unit. Removal of these heavy metals from wastewater occurs by uptake and by precipitation, the latter being particularly important in the cases of copper and zinc. The amount of heavy metal taken up by the microorganisms at equilibrium varies with influent concentration for the three metals studied. The values obtained range from 2.3 mg/g VSS for copper at 1 mg/L in the influent to 57.4 mg/g VSS for nickel at influent 25 mg/L. Soluble metal removal from wastewater increases in percentage with influent concentration, being higher for copper and lower for nickel. Experiments with mixtures of these metals have also been carried out.