Experimental investigation and modelling of diffusion dialysis process for regeneration of acidic pickling solutions

Pickling is one of the key steps in metal finishing industries, where HCl solutions are largely used thus generating significant amounts of spent waste solutions containing high concentrations of metals and acid. The recovery of acid from such waste solutions is thus one of the most beneficial steps for reducing the environmental and economical impact of these processes. Among several separation methods, diffusion dialysis (DD) is becoming more and more attractive thanks to the recent important advances in ion exchange membranes (IEMs) field and because of its clean nature and operational simplicity, low installation and operating costs and low energy consumption [1,2]. In the present work, a single-cell diffusion dialysis module equipped with a FumaTech Anion Exchange Membrane (AEM), operated in a batch mode, has been employed in order to study the effect of some parameters on the efficiency of HCl recovery from waste pickling acidic solutions. In addition, a mathematical model, capable of simulate and predict this process, has been also developed and validated with experimental information. The laboratory test-rig and procedures have been first evaluated and optimised by measuring salt and water fluxes with artificial NaCl solutions with different types of AEMs. Then, experiments with HCl solutions were carried out, at different compositions of diffusate and retentate streams, varying HCl concentration values in the range of 0.1-3 M. HCl and water osmotic fluxes were measured and their dependence on operating conditions was identified. Also the effect of the presence of selected iron salts were investigated in order to simulate the operation of the system when treating actual pickling solutions. In particular, the acid diffusion permeability as well as the water osmotic permeability tend to increase when increasing the solution concentration. In addition, an increasing HCl recovery is detected in the presence of iron chloride. References [1] Luo et al., Diffusion dialysis processes of inorganic acids and their salts: the permeability of different acidic anions, Separation and Purification Technology 78 (2011), 97-102 [2] Xu et al., Recovery of hydrochloric acid from the waste acid solution by diffusion dialysis, Journal of Hazardous Materials 165 (2009), 832-83

Economic Benefits of Waste Pickling Solution Valorization

An integrated hybrid membrane process, composed of a diffusion dialysis (DD), a membrane distillation (MD) and a reactive precipitation unit (CSTR), is proposed as a promising solution for the valorization and onsite recycling of pickling waste streams. An economic analysis was performed aiming to demonstrate the feasibility of the developed process with a NPV of about EUR 40,000 and a DPBP of 4 years. The investment and operating costs, as well as the avoided costs and the benefits for the company operating the plant, were analyzed with an extensive cost tracking exercise and through face-to-face contact with manufacturers and sector leaders. A mathematical model was implemented using the gPROMS modelling platform. It is able to simulate steady state operations and run optimization analysis of the process performance. The impact of key operating and design parameters, such as the set-point bath concentration and the DD and MD membrane areas, respectively, was investigated and the optimal arrangement was identified. Finally, operating variables and design parameters were optimized simultaneously in a nonlinear framework as a tradeoff between profitability and environmental impact. We show how the integration of new technologies into the traditional pickling industry could provide a significant benefit for the issues of process sustainability, which are currently pressing

Design of a novel membrane-integrated waste acid recovery process from pickling solution

Hydrochloric acid pickling is a common practice in steel manufacturing industry. During the process, acid is consumed to dissolve surface oxides and metals ions are accumulated in the solution, which becomes less effective with time. In addition, the costly and risky waste acid disposal is another issue affecting the hot-dip galvanizing industry. In this work, a novel sustainable waste acid recovery process from pickling solutions based on circular approach is proposed to tackle these issues. The innovative system allows (i) the continuous regeneration of pickling solutions to enhance process rate and performance and (ii) minimise the highly expensive and environmentally risky wastewater disposal. In this way, refilling pickling baths with fresh acid, as done in conventional operation, can be avoided and can be carried out continuously under optimal working conditions. Moreover, the recovery of valuable substances (e.g. metal hydroxide or salts solution) can be obtained as an additional benefit. Continuous treatment and regeneration of pickling solution can be accomplished by coupling diffusion dialysis (DD) and membrane distillation (MD) technologies with a reactive precipitation unit where iron ions can be separated from the zinc-rich solution, in order to recover valuable products. To this purpose, a steady state process simulator was developed to predict the operation of the proposed integrated process

Effective recovery of HCl and metals from pickling solutions by cutting-edge membrane technologies

The pickling process is an essential step in the hot-dip galvanizing process.It is performed by immersing manufacturedsteel pieces inacid bathsin order todissolve the oxidized layers. During the pickling process, acid attacks metal oxides on the surface, dissolving them in the pickling bath. Thus, the efficiency of the pickling liquor decreases due to the accumulation of metal salts and the consumption of free acid in the solution. When hydrochloric acid is used,ferrous chloride is producedduring the pickling treatment, reaching concentrations up to 250 g/l, while the acid concentration decreases by 75-85%. A pickling bath in this condition is considered spent [1] due to thevery low picklingrate, hence it needs to be replaced. In common industrial practice,part of the exhausted solution is withdrawn and replaced with fresh acid orwitha more concentrate solution to prolong the pickling bath life, while spentsolution is disposed asa waste.Disposal of the spentpickling solution strongly affects the hot-dip galvanizing industries footprintand costs, thus the recovery of acid is one of the most beneficial steps to reduce the environmental and economic impact.In particular, continuous regeneration of pickling solutions can enhance pickling rate and process performance, butalso reduce industrial wastewater disposal and chemicals consumption. The recovery and recycling of valuable compounds (e.g. acid, metals and water) can be accomplished by coupling two cutting-edge membrane technologies: diffusion dialysis (DD) and membrane distillation (MD) [2,3]. Membrane techniques are considered simple, effective and sustainable [1]and can be easily scaled from small to medium side installations.In the present work, a case study is presented, relevant tothe hot-dip galvanizing plant of TecnoZinco(Palermo, Italy).The site has a capacity of 20,000 tons per yearof treated steel. Starting from an accurate data mining, a Process Flow Diagram(PFD)of an integrated process that provides a continuous regeneration of pickling solution is proposed, within the framework of the EU-funded ReWaCEM project(www.rewacem.eu), with the final aim of buildinga pilot plant to be installedand operated in real environment. Asteady state process simulator for the integrated process has been developed, aiming to design, analyze and predict performance of the pilot unit. A parametric analysis of the model is performed varying hydrochloric acid in the stream going out from the pickling tank. Results presents the perspective operation of such plant, indicating the technical feasibility of the novel developed process

Experimental investigation and modeling of diffusion dialysis for HCl recovery from waste pickling solution

Hydrochloric acid recovery from pickling solutions was studied by employing a batch diffusion dialysis (DD) laboratory test-rig equipped with Fumasep membranes. The effect of main operating parameters such as HCl concentration (0.1–3 M) and the presence of Fe2+ (up to 150 g/l) was investigated to simulate the system operation with real industrial streams. The variation of HCl, Fe2+ and water flux was identified. When only HCl is present, a recovery efficiency of 100% was reached. In the presence of FeCl2, higher acid recovery efficiencies, up to 150%, were observed due to the so-called “salt effect”, which promotes the passage of acid even against its concentration gradient. A 7% leakage of FeCl2 was detected in the most severe conditions. An original analysis on water flux in DD operation has indicated that osmotic flux prevails at low HCl concentrations, while a dominant “drag flux” in the opposite direction is observed for higher HCl concentrations. A comprehensive mathematical model was developed and validated with experimental data. The model has a time and space distributed-parameters structure allowing to effectively simulate steady-state and transient batch operations, thus providing an operative tool for the design and optimisation of DD units

An integrated approach for HCl and metals recovery from waste pickling solutions: pilot plant design and operations

Continuous regeneration of industrial pickling solutions and recovery of valuable materials are implemented in a pilot-scale plant including diffusion dialysis, membrane distillation and reactive precipitation units. The main results of the preliminary assessment of on site operation are presented. Different hydrochloric acid concentration and metals composition were investigated and the performance of the system were analysed in terms of quality of recovered compounds, energy efficiency and environmental footprint

Modeling and Design of Membrane Process Recovery of HCl and Metals from Pickling Solutions

Abstract Hydrochloric acid pickling is one of the key steps in the hot-dip galvanizing process. It is a process widely used as a chemical pre-treatment method for cleaning, where metal surfaces with oxides are immersed into an acid solution. During the pickling process, the acid concentration decreases with time while the metal is accumulated. Thus, the efficiency of the pickling solution decreases and fresh solution must be used. Continuous regeneration of pickling solutions enhances pickling rate and process performance, but also minimises industrial wastewater disposal and chemicals consumption. The recovery and recycling process of valuable substances (e.g. acid and metals) can be accomplished by coupling diffusion dialysis (DD) and membrane distillation (MD) technologies [1,2]. The integrated process is based on a recovery of more than 80% of the free acid exiting from the pickling bath by passing through a selective anionic exchange membrane (in the DD), and then, its concentration by water evaporation through a hydrophobic membrane (in the MD) in order to be recycled in the pickling tank. The outlet stream from the diffusion dialysis, concentrated of metal salts, is fed to a reactive precipitation unit to recover iron as valuable product (iron hydroxide) by adding an alkaline reactant, whereas zinc salt is kept in the solution to be reused. In the present work, a steady state process simulator for the integrated process has been developed, in order to analyze and predict performances of a small pilot-scale unit to be installed and operated within a hot-dip galvanizing plant. A parametric analysis of the model is performed varying hydrochloric acid and iron concentration in the pickling tank. In this way, usual operations of withdrawing of partially exhausted solutions and refilling with fresh acid is avoided allowing to continuously operating under the optimal pickling conditions

Modeling and Design of Membrane Integrated Processes for HCl and Metals Recovery from Pickling Solutions

Hydrochloric acid pickling is a common practice in steel manufacturing industry. During the process, acid is consumed to dissolve surface oxides and metals are accumulated in the solution. This fact leads to a process efficiency decrease. Continuous regeneration of pickling solutions enhances process rate and performance, but also minimises the highly expensive and environmentally risky wastewater disposal. The recovery of valuable substances (e.g. acid and metals) can be accomplished by coupling diffusion dialysis (DD) and membrane distillation (MD) technologies. In the present work, a steady state process simulator for the integrated process has been developed. The aim is to analyze and predict performances of a small pilot-scale unit to be installed and operated within a hot-dip galvanizing plant. A parametric analysis of the model is performed varying the hydrochloric acid concentration. In this way, refilling with fresh acid, as done in the normal operations, is avoided and operations are carried out under the optimal working conditions

Experimental investigation and modelling of diffusion dialysis for the recovery of waste acid solutions

Pickling is widely used as a chemical pre-treatment method for cleaning metal surfaces before other surface treatments and it consumes large amount of acids and wate

Recovery of pickling acid solutions by membrane technology: the EU REWACEM Project

Resource recovery from industrial waste water by cutting edge membrane technologie