**1. Introduction**

In the recent years there has been a major concern to limit the risks associated with the manufacture of electrical and electronic equipment, the management of waste electrical and electronic equipment (WEEE) in order to minimize the negative impact on the environment [1–3]. In this regard, the European Union Regulations on Electronic Waste, WEEE Directive 2002/96/EC, EU WEEE DIRECTIVE 2012/19/EU and RoHs 2002/95/EC, regulate the responsibility of the member countries for the collection, use, recycling and recovery of electronic waste [4]. Rapid growth in production and technical development in electronics involves the accelerated replacement of outdated electronics equipment and accumulation of large amounts of harmful WEEE [5,6], including waste cathode-ray tube (CRT) glass from old televisions and computer monitors [7].

A CRT is composed of two different types of glass, from which one is used for the funnel and neck sections, characterized by high levels of lead oxide and another used for the screen which is typically a non-leaded glass that contains high levels of barium oxide [8]. Recycling of lead from waste CRT glass is an important issue because lead is classified as a neurotoxin that can accumulate in the soft tissues and bones, causing serious health issues [9–11]. The high content of lead oxide (23%) in CRT funnel glasses is an important factor that limits its landfill storage and the recycling process, as result many states have passed bans on putting CRTs in landfills or incinerators [12,13]. Additionally, CRT funnel glass, due to its composition, is unsuitable for applications where metal oxides could leach into food products or ground water [14].

**Citation:** Imre-Lucaci, Á.; Fogarasi, M.; Imre-Lucaci, F.; Fogarasi, S. Chemical–Electrochemical Process Concept for Lead Recovery from Waste Cathode Ray Tube Glass. *Materials* **2021**, *14*, 1546. https:// doi.org/10.3390/ma14061546

Academic Editors: Rossana Bellopede and Lorena Zichella

Received: 17 February 2021 Accepted: 18 March 2021 Published: 22 March 2021

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Conventional CRT glass recycling is carried out in a closed-loop, where waste glass, after an appropriate removal of metal and luminophore contaminants, is utilized during manufacturing of new CRTs [15,16]. However, the above-mentioned recycling method is insufficient, as technology develops and modern liquid crystal display (LCD), plasma or light-emitting diode (LED) screens are introduced, the demand for CRT glass decreases [17]. As a result, it is necessary to provide the industry with new technical solutions for the processing of waste glass which led to other products than CRTs [18]. The most common applications of the waste glass are related to the manufacturing of different products like conventional ceramics, aggregates and cements [19,20]. Some of the technologies involve high temperature treatment of the CRT waste glass leading to ceramic or glass composites used in the construction industry, mainly to manufacture bricks and roof tiles [21,22]. The CRT waste glass cullet can be also used in the metallurgical industry to produce ferro-silicates in the form of slag [23]. Other methods have also been developed for the use of waste CRT glass in the production of floor coverings and chemical resistant compounds [24].

Unfortunately, the amount of waste material that can be recycled in the above mentioned technologies is limited due to the fact that waste CRT glass is used without preliminary separation of harmful components, involving higher environmental risks, operation and maintenance costs [25,26]. In order to overcome this drawback, associated with waste CRT glass recycling, there have been attempts to remove the hazardous components like lead employing different hydrometallurgical and pyrometallurgical processes [27–29]. These processes present some major disadvantages like insufficient lead removal efficiency and polluting byproducts, which can be more harmful than the treated waste material [30]. Moreover, many of the studies presented in the literature lack a comprehensive overview, by not assessing both the technical performance and environmental impact of the processes, which is necessary to draw global conclusions [29,31].

In view of the above discussion, the recovery of lead from waste CRT glasses was achieved by acetic acid leaching of Pb coupled with the simultaneous electrowinning of a high purity Pb deposit and regeneration of the leaching agent. The novel process concept defined and assessed in the current paper ensures high technical performance with a low environmental impact, based on the influence of acetic acid concentration, recirculation flow rate and current density on different key performance indicators and GEIs values.
