DEVELOPMENT AND MODELING OF MEMBRANE PROCESSES FOR THE REGENERATION OF ACID PICKLING SOLUTIONS

The doctoral thesis focuses on a novel integrated process for the recovery and valorisation of acid and metal salts present in the waste solutions of the pickling process. The proposed process is based on the integration of two innovative membrane technologies, the Diffusion Dialysis and the Membrane Distillation, coupled with a reactive precipitation section. This hybrid process allows the recovery and the enhancement of waste solutions, as well as optimal operating conditions for the continuous pickling process, thus improving its efficiency. Hydrochloric acid recovery was assessed through a detailed study on the Diffusion Dialysis process by implementing a wide experimental campaign using artificial solutions produced in laboratory, in order to understand and characterize the system. A mathematical model was developed with time and space distributed-parameters structure for the effective simulation of steady state and transient batch operations, thus providing an operative tool for the design and optimization of DD units. Selective separation of metal salts was reached by precipitating ferric hydroxide and maintaining ammonium and zinc chlorides in solution, which can be used as fluxing solution in the galvanizing process itself, thus implementing the typical Circular Economy concept. The feasibility of the proposed process is demonstrated through the use of a purposely developed process simulator able to predict steady state operation of the integrated process and to perform sensitivity analysis for the identification of the best operating conditions of the system. An experimental campaign was carried out with a demonstrator unit, jointly designed and constructed by Fraunhofer ISE (Freiburg, Germany), eventually installed in the real industrial environment of Tecnozinco s.r.l hot-dip galvanizing plant in Carini, Sicily. The campaign assessed the integration performance of the different units and the process reliability, resulting in a minimization of spent pickling solution disposal and in high quality recovered compounds. An engineering economic analysis was carried out in order to assess the economic feasibility of the proposed process. The economic model was implemented in the gPROMS simulation platform and was used to conduct an optimization analysis, defining the optimal operational and design conditions for which the process is more profitable and performing. The process simulator was also used to provide a scale-up of the demonstrator plant. The results have shown that the process has a good potential for industrial implementation, thanks to the economic and environmental benefits

Combining Membrane and Zero Brine Technologies in Waste Acid Treatment for a Circular Economy in the Hot‑Dip Galvanizing Industry: A Life Cycle Perspective

An innovative approach of combining membrane and zero brine technologies for a joint treatment of industrial liquid waste is investigated regarding its environmental impacts compared to the existing liquid waste treatment. The object of investigation is the generation of waste acid solution by a hot dip galvanizing plant in Sicily, Italy. The waste acid solution contains hydrochloric acid, iron and zinc, which makes it a hazardous waste according to EU classifcations. Environmental impacts are studied for two scenarios in the Tecnozinco hot-dip galvanizing plant in Sicily, Italy: (i) the current process of pickling with linear disposal of waste acid and (ii) the pickling combined with in-situ treatment of the waste acid using a combination of difusion dialysis (DD), membrane distillation (MD) and a precipitation reactor. Results are obtained via an attributional life cycle assessment (LCA) approach focusing on the water footprint profle of the process. The linear disposal path creates signifcant costs, environmental burdens and risks during the 1500 km transport of hazardous liquid waste. The combination of DD and MD, complemented with a zero-brine precipitation reactor, closes internal material loops, could save local water resources and reduces costs as well as environmental impacts. Reduction potentials of 70–80% regarding most LCA impact categories can be expected for the application of the novel technology combination supporting the galvanizing pre-treatment process under study. Therefore, the application of such technology on the way forward to a more circular economy is recommended from an environmental viewpoint, especially in process plants similar to the investigated one

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

Diffusion Dialysis for Separation of Hydrochloric Acid, Iron and Zinc Ions from Highly Concentrated Pickling Solutions

Acid recovery from pickling waste solutions is an important step to enhance hot-dip-galvanizing industry process sustainability. Diffusion dialysis (DD) can be used to separate acids and heavy metals (e.g., iron and zinc) from pickling waters, promoting the circular use of such raw materials. In the present study, a laboratory scale unit operating in batch and a continuous large scale unit, both equipped with Fumasep anionic exchange membranes, were tested. Results obtained show that zinc and iron concentration affect the HCl recovery in opposite ways. Iron chlorides enhance acid recovery, while zinc chlorides considerably tend to diffuse through the membrane because of negatively charged chloro-complexes formation and slightly reduce the acid diffusion. A multi-components mathematical model, with a time-dependent and distributed-parameters architecture, was adopted enabling the prediction of operations with hydrochloric acid, zinc, and iron metals both in batch and in continuous dialyzers. As a result, a good comparison between model simulations and experiments was achieved in both configurations

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

Diffusion Dialysis for Separation of Hydrochloric Acid, Iron and Zinc Ions from Highly Concentrated Pickling Solutions

Acid recovery from pickling waste solutions is an important step to enhance hot-dip-galvanizing industry process sustainability. Diffusion dialysis (DD) can be used to separate acids and heavy metals (e.g., iron and zinc) from pickling waters, promoting the circular use of such raw materials. In the present study, a laboratory scale unit operating in batch and a continuous large scale unit, both equipped with Fumasep anionic exchange membranes, were tested. Results obtained show that zinc and iron concentration affect the HCl recovery in opposite ways. Iron chlorides enhance acid recovery, while zinc chlorides considerably tend to diffuse through the membrane because of negatively charged chloro-complexes formation and slightly reduce the acid diffusion. A multi-components mathematical model, with a time-dependent and distributed-parameters architecture, was adopted enabling the prediction of operations with hydrochloric acid, zinc, and iron metals both in batch and in continuous dialyzers. As a result, a good comparison between model simulations and experiments was achieved in both configurations

AN INTEGRATED APPROACH FOR THE HCl AND METALS RECOVERY FROM WASTE PICKLING SOLUTIONS: PILOT PLANT DESIGN AND OPERATIONS

Pickling is one of the key steps in the hot-dip galvanizing process, where HCl solutions are largely used to remove metal oxides from metallic surfaces, thus generating spent waste liquors containing high concentrations of metals and acid. Disposal of the industrial pickling waste dramatically affects the hot-dip galvanizing industry economics and environmental footprint. Thus, reducing strong acid waste disposal is one of the most beneficial steps to enhance the process sustainability. Moreover, the continuous regeneration of pickling solutions enhances pickling rate and process performance, also minimizing industrial wastewater disposal and chemicals consumption promoting the circular use of such raw materials. In this work we propose the recovery and recycling process of valuable substances (e.g. acid, metals and aqueous streams) from pickling solutions by coupling two innovative cutting-edge membrane technologies: diffusion dialysis (DD) and membrane distillation (MD). A pilot-scale unit was designed and build following extensive experimental and simulative campaigns carried out the ReWaCEM project. The Demo system consists of a DD module, where HCl is recovered from the waste pickling acid solution, a MD module, where the recovered HCl is concentrated, and a reactive precipitation section, where Fe ions, exiting with the metals-rich retentate brine from the diffusion dialysis, is recovered as iron hydroxide. In this latter stage, also an ammonium hydroxide/zinc chloride solution is produced, to be reused in the fluxing bath of the hot-dip galvanizing plant. The fully-automatized pilot unit is able to operate in continuous, guaranteeing the operation at the optimal pickling conditions in terms of HCl and Fe concentration. Moreover, the use of waste heat (for MD operation) further contributes to enhance process sustainability. The main results of the on-site pilot plant operation are presented. Several experiments were carried out to assess the system operability and the feasibility of fully reducing spent pickling solution disposal and recovering valuable materials. Results have shown that high recovery of acid (80%) can be achieved in the Diffusion Dialysis unit since the presence of iron ions in solution further increases acid recovery, although significant Zn leakage occurs through the membrane. On the other side, the performance of MD is good when operating in the lower range of metals concentration, while it suffers when metal salts are present in large quantities (due to poorer rejection in the DD unit) due to the lower water vapor pressure. On the basis of this first pilot campaign an optimized configuration for the system has been developed and will be tested in the next months

Metals Recovery from Waste Pickling Solutions by Reactive Precipitation

Pickling is one of the most important steps in steel manufacturing industry. During the process, an acid reacts with the surface oxides causing metal ions accumulation in the pickling solution. Disposal of the waste acid represents a critical issue for the hot-dip galvanizing industry in terms of environmental damage and high costs. Recovering of the main products by using an integrated process, with the perspective of a circular approach, could minimize the wastewater production, leading to reinvigorate this industrial sector economy. In this context, recovery of the metal ions mainly present in the pickling solution, such as Fe and Zn, becomes a critical issue. In this work, the reactive precipitation process reliability was proved through lab-scale experiments, in order to collect information for the design of a pilot-plant to be installed in the Tecnozinco SrL (Carini, Italy) hot-dip galvanizing plant. Experiments were carried out in a continuous stirred tank reactor by feeding the acidic metals-rich stream, an alkaline reactant and an oxidant. The quantity of Fe in the outlet solution and its speciation in the precipitate were detected to evaluate the recovery efficiency and the process quality, whereas Zn concentration in the precipitated was detected for determining the product purity. Some key parameters, such as temperature and pH, were studied by varying inlet streams flow rates. A very effective metals separation was observed by obtaining Fe(III) hydroxide at a high purity of 99 %. Zn ions were successfully separated by keeping them in solution with the aim of generating a zinc/ammonium chloride stream, to be reused in the fluxing baths of the hot-dip galvanizing plant

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

Continuous regeneration of industrial pickling solutions and recovery of valuable materi-als are implemented in a pilot-scale plant including diffusion dialysis (DD), where HCl isrecovered, membrane distillation (MD), where HCl is concentrated, and reactive precipita-tion (CSTR), where metal ions are recovered in different forms. The integration of the threeprocesses allows to minimize waste streams generation and to accomplish a closed-loopprocess, thus increasing the environmental sustainability and economic impact of the gal-vanizing industry. Process reliability was proved through the operation of a demonstratorin the real industrial environment of the Tecnozinco SrL hot-dip galvanizing plant (Carini,Italy), assessing the actual performance in fully reducing spent pickling solution disposaland recovering useful compounds. Tests were conducted firstly with synthetic solutionsand then with real waste liquors from the pickling plant. A high acid recovery (80%) can beachieved in the diffusion dialysis unit and quantitative metals separation was accomplished,with iron hydroxide produced at 99% purity. The membrane distillation performance sufferswhen metal salts are present in large quantities, due to the “salting out” effect, resultingin reduced water vapor pressure, though the use of available low grade waste heat allowsenergy-sustainable operation of the MD

Metals recovery from waste pickling solutions by reactive precipitation

Pickling is one of the most important steps in steel manufacturing industry. During the process, an acid reacts with the surface oxides causing metal ions accumulation in the pickling solution. Disposal of the waste acid represents a critical issue for the hot-dip galvanizing industry in terms of environmental damage and high costs. Recovering of the main products by using an integrated process, with the perspective of a circular approach, could minimize the wastewater production, leading to reinvigorate this industrial sector economy. In this context, recovery of the metal ions mainly present in the pickling solution, such as Fe and Zn, becomes a critical issue. In this work, the reactive precipitation process reliability was proved through lab-scale experiments, in order to collect information for the design of a pilot-plant to be installed in the Tecnozinco SrL (Carini, Italy) hot-dip galvanizing plant. Experiments were carried out in a continuous stirred tank reactor by feeding the acidic metals-rich stream, an alkaline reactant and an oxidant. The quantity of Fe in the outlet solution and its speciation in the precipitate were detected to evaluate the recovery efficiency and the process quality, whereas Zn concentration in the precipitated was detected for determining the product purity. Some key parameters, such as temperature and pH, were studied by varying inlet streams flow rates. A very effective metals separation was observed by obtaining Fe(III) hydroxide at a high purity of 99 %. Zn ions were successfully separated by keeping them in solution with the aim of generating a zinc/ammonium chloride stream, to be reused in the fluxing baths of the hot-dip galvanizing plan