Industrial symbiosis: high purity recovery of metals from Waelz sintering waste by aqueous SO2 solution

Sintering operation in the production of Zn, Cd, and Pb by Waelz process produces a powdery waste containing mainly (about 70%) ZnO, CdO, and PbO. The waste may be referred to as Waelz sintering waste (WSW). The aim of this study is to develop a process for the separation and recovery of the metals from WSW with high purities. The process is based on the dissolution of the WSW in aqueous SO2 solution. The research reported here concentrated on the effect of some important operational parameters on dissolution process. The parameters investigated and their ranges were as follows: SO(2) gas flow rate (V); 38-590 ml/min, stirring speed (W); 100-1000 rpm, reaction temperature (T); 13-60 degrees C, reaction time (t); 1-16 min, and solid-liquid ratio (S/L); 0.1-0.5 g/ml. The results showed that the dissolution rate increased with increasing W, V, and S/L and decreasing T. The best dissolution conditions were found to be V=325 ml/min, W=600 rpm, t=6 min, T=21 degrees C, and S/L=0.1g/ml. Separation of Zn from Cd involved precipitation of ZnSO3 from a mixture solution. The best pH level for the precipitation was observed to be 6.     

Energy recovery from waste incineration: economic aspects

If we consider the desirability of reducing fossil fuel consumption, together with the increasing production of combustible solid wastes, there is clearly a need for waste treatment systems which achieve both volume reduction and energy recovery. Direct incineration method is one such system. The aim of this work was to analyze the municipal solid waste incineration situated in the Province of Turin (Piedmont, North Italy), especially its economical effects in consequence of the energy recovery that can be achieved. In order to perform this analysis, two kinds of energy recovery have been studied: electric energy (electrical configuration) only, and both electric and thermal energy (cogenerative configuration). So after a reconstruction of the economic situation, by considering all the costs and revenues, for both the possible energetic configurations the correspondence between the environmental convenience (that was evaluated in a previously work) and the economic convenience has been defined. The main obtained results highlight that currently the environmental convenience corresponds to the cogenerative configuration; instead the economical convenience in the actual condition corresponds to the only electric configuration. Anyway, by working on the thermal energy price, it is possible to obtain at the same time an environmental and economic convenience.     

Arsenic extraction from nonferrous metals industry waste

We have formulated physicochemical principles of environmentally safe technologies for processing typical arsenic-containing nonferrous metals production waste via acid and alkaline stripping and chemical reduction. Our results indicate that the most efficient process for the preparation of crude arsenic compounds is sulfuric acid extraction of cake components. Detailed studies, using an arsenic-calcium cake as a test system, demonstrate that nonferrous metals production wastes are promising raw materials for the preparation of high-purity arsenic, its compounds, and other valuable metals.     

Cleaning of waste smelter slags and recovery of valuable metals by pressure oxidative leaching

Huge quantities of slag, a waste solid product of pyrometallurgical operations by the metals industry are dumped continuously around the world, posing a potential environmental threat due to entrained values of base metals and sulfur. High temperature pressure oxidative acid leaching of nickel smelter slags was investigated as a process to facilitate slag cleaning and selective dissolution of base metals for economic recovery. Five key parameters, namely temperature, acid addition, oxygen overpressure, solids loading and particle size, were examined on the process performance. Base metal recoveries, acid and oxygen consumptions were accurately measured, and ferrous/ferric iron concentrations were also determined. A highly selective leaching of valuable metals with extractions of >99% for nickel and cobalt, >97% for copper, >91% for zinc and <2.2% for iron was successfully achieved for 20 wt.% acid addition and 25% solids loading at 200-300 kPa O(2) overpressure at 250 degrees C in 2h. The acid consumption was measured to be 38.5 kg H(2)SO(4)/t slag and the oxygen consumption was determined as 84 kg O(2)/t slag which is consistent with the estimated theoretical oxygen consumption. The as-produced residue containing less than 0.01% of base metals, hematite and virtually zero sulfidic sulfur seems to be suitable for safe disposal. The process seems to be able to claim economic recovery of base metals from slags and is reliable and feasible.     

Electrochemical arsenic extraction from nonferrous metals industry waste

We have developed physicochemical approaches to processing of arsenic-containing nonferrous metals industry waste with the use of sulfuric acid stripping followed by electrochemical arsenic extraction. Our results indicate the possibility of producing crude and high-purity arsenic; metallic zinc; and Sn, Pb, Sb, Cd, and Cu concentrates. A combined process has been developed for the preparation of 99.9999%-pure arsenic.     

Low-cost adsorbents for heavy metals uptake from contaminated water: a review

In this article, the technical feasibility of various low-cost adsorbents for heavy metal removal from contaminated water has been reviewed. Instead of using commercial activated carbon, researchers have worked on inexpensive materials, such as chitosan, zeolites, and other adsorbents, which have high adsorption capacity and are locally available. The results of their removal performance are compared to that of activated carbon and are presented in this study. It is evident from our literature survey of about 100 papers that low-cost adsorbents have demonstrated outstanding removal capabilities for certain metal ions as compared to activated carbon. Adsorbents that stand out for high adsorption capacities are chitosan (815, 273, 250 mg/g of Hg(2+), Cr(6+), and Cd(2+), respectively), zeolites (175 and 137 mg/g of Pb(2+) and Cd(2+), respectively), waste slurry (1030, 560, 540 mg/g of Pb(2+), Hg(2+), and Cr(6+), respectively), and lignin (1865 mg/g of Pb(2+)). These adsorbents are suitable for inorganic effluent treatment containing the metal ions mentioned previously. It is important to note that the adsorption capacities of the adsorbents presented in this paper vary, depending on the characteristics of the individual adsorbent, the extent of chemical modifications, and the concentration of adsorbate.     

Development of electronic materials from industrial waste red mud

The current research work presents the preparation and characterization of some new electronic materials using bismuth oxide (Bi₂O₃) and industrial waste red mud in different proportion by weight using a cost-effective mixed-oxide technique. Preliminary X-ray structural analysis exhibits the formation of compounds with structure analogous to that of BiFeO₃ compound along with some impurity phases. Studies of dielectric parameters (ε_r and tanδ) of these compounds as a function of temperature and frequency exhibit that they are almost temperature independent in the low temperature range and possess high relative permittivity with low loss in the high temperature range. Detailed studies of impedance and related parameters exhibit that the electrical properties of these materials are strongly dependent on temperature, and bear a good correlation with their microstructures. The bulk resistance, evaluated from complex impedance spectra, is found to be decreasing with rise in temperature, exhibiting a typical negative temperature co-efficient of resistance (NTCR)—type behavior similar to that of semiconductors. Studies of electric modulus indicate the presence of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation. The low leakage current and NTCR behavior of the sample have been verified from I–V characteristics. The nature of variation of dc conductivity with temperature confirms the Arrhenius and NTCR behavior in the material. The ac conductivity spectra show a typical-signature of an ionic conducting system, and are found to obey Jonscher’s universal power law.     

The ultrasonically assisted metals recovery treatment of printed circuit board waste sludge by leaching separation

This paper provides a practical technique that realized industrial scale copper and iron separation from printed circuit board (PCB) waste sludge by ultrasonically assisted acid leaching in a low cost, low energy consumption and zero discharge of wastes manner. The separation efficiencies of copper and iron from acid leaching with assistance of ultrasound were compared with the one without assistance of ultrasound and the effects of the leaching procedure, pH value, and ultrasonic strength have been investigated in the paper. With the appropriate leaching procedure, a final pH of 3.0, an ultrasonic generator power of 160 W (in 1 l tank), leaching time of 60 min, leaching efficiencies of copper and iron had reached 97.83% and 1.23%, respectively. Therefore the separation of copper and iron in PCB waste sludge was virtually achieved. The lab results had been successfully applied to the industrial scaled applications in a heavy metal recovery plant in city of Huizhou, China for more than two years. It has great potentials to be used in even the broad metal recovery practices.     

Adsorption of heavy metals from wastewater with waste activated sludge

Abstract

The purpose of this study is the investigation of the adsorption of heavy metals from wastewater with waste activated sludge (WAS) so as to increase the operational flexibility of activated sludge processes for the shock loading problems of heavy metals. By contacting the raw wastewater with WAS, before it entered the activated sludge process unit, some heavy metals in the wastewater were removed, and the pH value of the acidic wastewater rose. Five metals, Cu, Zn, Ni, Cd and Pb, were studied, some factors which affected this biosorption phenomena were investigated, and expressions of the adsorption isotherms were discussed. A semi‐empirical mass transfer‐adsorption model was developed to describe the kinetic experimental data.     

Technologies and logistics for phosphorus recovery from livestock waste

Phosphorus (P) runoff from livestock waste can trigger algal blooms that adversely affect aquatic life and human health. One strategy to mitigate this problem is to install nutrient recovery technologies that concentrate and mobilize nutrients from nutrient-rich regions to nutrient-deficient ones. We present supply chain design formulations to identify optimal types and locations for P recovery technologies. The formulations capture trade-offs in transportation costs, technology efficiency, investment/operational costs, revenue collected from different recovered products (struvite and nutrient cakes), and environmental impact. Our computational framework is used to analyze the impact of different scenarios for market prices of recovered products, recovery yields, and remediation costs. We find that transportation of waste alone (without any processing) can achieve significant reductions in environmental impact at low cost, but cannot achieve economic sustainability in the long run due to the lack of direct revenue streams. Mechanical separation technologies that recover P in the form of nutrient cakes are low-cost solutions that can achieve high environmental benefits and reduced transportation costs, but revenues are also limited due to low values of the cakes. Struvite crystallization in fluidized beds is found to be a highly attractive option under current struvite prices, but economic sustainability is strongly dependent on yield recoveries (which are currently highly uncertain).     

Recovery of metals from waste printed circuit boards by a mechanical method using a water medium

Research on the recycling of waste printed circuit boards (PCB) is at the forefront of environmental pollution prevention and resource recycling. To effectively crush waste PCB and to solve the problem of secondary pollution from fugitive odors and dust created during the crushing process, a wet impacting crusher was employed to achieve comminution liberation of the PCB in a water medium. The function of water in the crushing process was analyzed. When using slippery hammerheads, a rotation speed of 1470 rpm, a water flow of 6 m³/h and a sieve plate aperture of 2.2 mm, 95.87% of the crushed product was sized less than 1 mm. 94.30% of the metal was in this grade of product. Using smashed material graded −1 mm for further research, a Falcon concentrator was used to recover the metal from the waste PCB. Engineering considerations were the liberation degree, the distribution ratio of the metal and a way to simplify the technology. The separation mechanism for fine particles of different densities in a Falcon concentrator was analyzed in detail and the separation process in the segregation and separation zones was deduced. Also, the magnitude of centrifugal acceleration, the back flow water pressure and the feed slurry concentration, any of which might affect separation results, were studied. A recovery model was established using Design-Expert software. Separating waste PCB, crushed to −1 mm, with the Falcon separator gave a concentrated product graded 92.36% metal with a recovery of 97.05%. To do this the reverse water pressure was 0.05 MPa, the speed transducer frequency was set at 30 Hz and the feed density was 20 g/l. A flow diagram illustrating the new technique of wet impact crushing followed by separation with a Falcon concentrator is provided. The technique will prevent environmental pollution from waste PCB and allow the effective recovery of resources. Water was used as the medium throughout the whole process.     

大豆低聚糖纳滤连续浓缩过程的控制

提出了一种利用纳滤膜来连续浓缩大豆低聚糖的新工艺.介绍了20 t/h大豆低聚糖纳滤连续浓缩工艺流程及控制要求,设计了基于PLC的过程控制系统.控制系统结构采用Siemens的TP170B触摸屏作为人机界面,S7 200 PLC、DR 20调节器和MM 430变频器作为控制核心.通过在山东谷神应用结果表明,该工艺流程经济适用、运行稳定可靠、自动化程度高,能够满足连续生产的要求,提高了膜分离装置的运行效率.     

New processes for recovery of acetic acid from waste water

This paper addresses an industrially important problem of acetic acid recovery from a waste water stream via reactive distillation. The presence of a three-phase regime on the column stages due to a liquid–liquid phase split between aqueous and organic phases is a typical characteristic of this process. A modern modeling approach is presented to detect the existence of potential phase splitting in this column. A good agreement of a phase splitting model with the literature data has been shown. A theoretical study for the recovery of acetic acid from its 30 wt% aqueous solution by esterification with n-butanol is presented. Alternate column structures were investigated and two structures rendering theoretically close to 100% conversion of acetic acid were identified. The dynamic simulations were performed on proposed structures to see transient responses wrt. to common process disturbances. The work was originally presented at the PRES-2006 (27–31 August) conference in Prague, Czech Republic.     

Hydrogen recovery from the thermal plasma gasification of solid waste

Thermal plasma gasification has been demonstrated as one of the most effective and environmentally friendly methods for solid waste treatment and energy utilization in many of studies. Therefore, the thermal plasma process of solid waste gasification (paper mill waste, 1.2 ton/day) was applied for the recovery of high purity H(2) (>99.99%). Gases emitted from a gasification furnace equipped with a nontransferred thermal plasma torch were purified using a bag-filter and wet scrubber. Thereafter, the gases, which contained syngas (CO+H(2)), were introduced into a H(2) recovery system, consisting largely of a water gas shift (WGS) unit for the conversion of CO to H(2) and a pressure swing adsorption (PSA) unit for the separation and purification of H(2). It was successfully demonstrated that the thermal plasma process of solid waste gasification, combined with the WGS and PSA, produced high purity H(2) (20 N m(3)/h (400 H(2)-Nm(3)/PMW-ton), up to 99.99%) using a plasma torch with 1.6 MWh/PMW-ton of electricity. The results presented here suggest that the thermal plasma process of solid waste gasification for the production of high purity H(2) may provide a new approach as a future energy infrastructure based on H(2).     

Zinc recovery and waste sludge minimization from chromium passivation baths

This work reports the feasibility of applying emulsion pertraction technology (EPT) aiming at zinc recovery and waste minimization in the zinc electroplating processes that include Cr (III) passivation. The assessment consists of firstly the lifetime extension of the passivation baths by selective removal of the tramp ions zinc and iron, and secondly, the recovery of zinc for further reuse. Spent passivation baths from a local industry were tested, being the major metallic content: Cr³⁺ 9000 mg L⁻¹, Zn²⁺ 12,000 mg L⁻¹, Fe³⁺ 100 mg L⁻¹. Working in a Liqui-Cel hollow fiber membrane contactor and using the extractant bis(2,4,4-trimethylpentyl) phosphinic acid, reduction of zinc and iron concentrations below 60 mg L⁻¹ and 2 mg L⁻¹, respectively were obtained, while trivalent chromium, the active metal that generates the passivation layer, was retained in the baths. Zinc was selectively transferred to an acidic stripping phase that in the experimental time reached a concentration of 157,000 mg L⁻¹. Zinc recovery by electrowinning from the acidic stripping phase without any pretreatment of the electrolyte solution provided a purity of 98.5%, matching the lower commercial zinc grade. As a result of the extension of the life time of the passivation bath, significant environmental advantages are derived such as minimization of the volume of hazardous wastes and savings in the consumption of raw materials.     

Heavy metal adsorption onto agro-based waste materials: a review

Adsorption has been proved to be an excellent way to treat industrial waste effluents, offering significant advantages like the low-cost, availability, profitability, easy of operation and efficiency. Biosorption of heavy metals from aqueous solutions is a relatively new process that has proven very promising in the removal of contaminants from aqueous effluents. Biosorption is becoming a potential alternative to the existing technologies for the removal and/or recovery of toxic metals from wastewater. The major advantages of biosorption technology are its effectiveness in reducing the concentration of heavy metal ions to very low levels and the use of inexpensive biosorbent materials. Metal adsorption and biosorption onto agricultural wastes is a rather complex process affected by several factors. Mechanisms involved in the biosorption process include chemisorption, complexation, adsorption-complexation on surface and pores, ion exchange, microprecipitation, heavy metal hydroxide condensation onto the biosurface, and surface adsorption.     

Estimation of waste heat and its recovery potential from energy-intensive industries

Clean Technologies and Environmental Policy - The recovery and reuse of waste heat offers a significant opportunity for any country to reduce its overall primary energy usage. Reuse of waste heat...     

Factors affecting hazardous waste solidification/stabilization: a review

Solidification/stabilization is accepted as a well-established disposal technique for hazardous waste. As a result many different types of hazardous wastes are treated with different binders. The S/S products have different property from waste and binders individually. The effectiveness of S/S process is studied by physical, chemical and microstructural methods. This paper summarizes the effect of different waste stream such as heavy metals bearing sludge, filter cake, fly ash, and slag on the properties of cement and other binders. The factors affecting strength development is studied using mix designs, including metal bearing waste alters the hydration and setting time of binders. Pore structure depends on relative quantity of the constituents, cement hydration products and their reaction products with admixtures. Carbonation and additives can lead to strength improvement in waste-binder matrix.     

Hazardous waste generation and management in China: a review

Associated with the rapid economic growth and tremendous industrial prosperity, continues to be the accelerated increase of hazardous waste generation in China. The reported generation of industrial hazardous waste (IHW) was 11.62milliontons in 2005, which accounted for 1.1% of industrial solid waste (ISW) volume. An average of 43.4% of IHW was recycled, 33.0% was stored, 23.0% was securely disposed, and 0.6% was discharged without pollution controlling. By the end of 2004, there were 177 formal treatment and disposal centers for IHW management. The reported quantity of IHW disposed in these centers was only 416,000tons, 65% of which was landfilled, 35% was incinerated. The quantity of waste alkali and acid ranked the first among IHW categories, which accounted for 30.9%. And 39.0% of IHW was generated from the raw chemical materials and chemical products industry sectors. South west China had the maximum generation of IHW, accounted for 40.0%. In addition, it was extrapolated that 740,000tons of medical wastes were generated per year, of which only 10% was soundly managed. The generation of discarded household hazardous waste (HHW) is another important source of hazardous waste. A great proportion of HHW was managed as municipal solid waste (MSW). Hazardous waste pollution controlling has come into being a huge challenge faced to Chinese environmental management.     

Efficiency of a zeolitized pumice waste as a low-cost heavy metals adsorbent

The unextracted residue obtained after a countercurrent two-step extractive process of silica from pumice lapillus, at 100 degrees C and room pressure, has been found mainly crystallized to the pseudo-cubic form typical of zeolite P. This residue could be active as a low-cost agent for the removal of heavy metals from wastewater. In this paper the removal capacity of six metallic cations (i.e. Cu(2+), Ni(2+), Zn(2+), Cd(2+), Pb(2+) and Cr(3+)) was studied in a stirred batch reactor. Results obtained showed that the removal of metal ions (100-500mgg(-1)) from wastewater is achieved in a short time and the concentration lowered under the legal limits. The adsorption mechanism mainly involves an ionic exchange between sodium ions from the solid phase and heavy metals in solution. However, if wastewater was accompanied by free acidity, it first should be neutralized to pH 4-5 to prevent zeolite destruction.