No matter which recycling technology is to be adopted, the batteries must always be drained before they enter the recycling process, since the acidic electrolyte produces several complications in the lead fusion-reduction. After drainage, batteries may or may not be broken, depending on the specific recycling process adopted.
Classic methodologies of lead recycling processes, including Water-Jacket Blast furnaces, reverberatory furnaces, electric arc furnaces, and short and long rotary furnaces, do not require battery breakage before the smelting process. The drained batteries are entered directly into the recycling process since pyrometalurgic techniques accept organic materials and other substances, which are burned or incorporated into the slag.
However, processes in which the batteries are broken prior to the recycling process are preferable due to:
(a) increase in the percentage lead production and decrease in the slag formation;
(b) possibility of soft lead production as well as antimonial lead;
(c) possibility of polypropylene recovery;
(d) simplification of furnace smoke treatment;
(e) pyrometalurgical techniques cannot accept the acid from battery electrolyte.
Furthermore, improvements in the battery production industry lead ultimately to the production of sealed batteries and other systems which are no longer easily drained. Therefore, an increasing amount of batteries must be broken before entering the recycling process.
Before the 1960’s, batteries were opened mainly by ax just when the recycling process demanded a lower organic content into the furnace otherwise they were inserted directly into the furnace. Although this situation has changed in most countries, especially in the developed ones, unfortunately it has not in most developing countries. It must be stressed, however, that manual breaking of batteries should be avoided at all costs, not only because it is a major source of human health contamination but also because it is an environmentally unsound management of these wastes. Nevertheless, some modern smelting plants still require manual breaking of big industrial batteries that cannot be broken by normal apparatus due to its size. If such technique is needed, all proper measures must be taken to provide protection to the workers and the environment.
During the decades of 60’s and 70’s, the battery breaking evolved into a mechanical guillotine or saw that greatly reduced human contact with the breakage process. They were also supplemented by automatic feed and were the first examples of entirely mechanized systems, some of them are still in use.
From the 1980 onwards, most of the modern smelting plants were adopting a totally mechanized system in which the batteries were received, transported and broken into sufficiently small pieces in order to separate the battery constituents:
The modern battery breaking process starts with the arrival of used batteries at the recycling facility. Human contact is usually minimized as much as possible so the used batteries are received and directed to the breaking apparatus by means of automatic mats or small wagons whenever possible.
Once the batteries arrive at the breaking machine, they are processed in the hammer mills, or other crushing mechanisms, that break them into small pieces. This breakage procedure ensures that all components, such as lead plates, connectors, plastic boxes and acid electrolyte are easily separated in the subsequent steps.
After breakage, the lead oxides and sulfates are separated from the other materials by gravity in water by a system of moving mesh conveyers. After separation, they are directed to a furnace, in case of pyrometalurgic techniques, or for other processes, for example hydrometallurgical techniques.
After the first rough breakage, sometimes there are other crushing mechanisms that further decrease the size of the remaining materials. The metallic parts, including lead plates, grids, connectors and terminals, are then separated from the organic parts, which include boxes, either polypropylene, ebonite or PVC, in the form of the plate separators, etc., by means of density difference in hydraulic separators which differ from process to process.
Other processes, through use of density properties and hydraulic mechanisms, separate the broken battery pieces in three different layers: the first one is constituted of light fractions such as plastics, the second is constituted of fine granular pieces of lead oxide and sulfates and the third one is the heavy layer consisting of lead plates, connectors, etc. This method, therefore, lacks the filtration step in order to remove lead compounds prior to plastic recovery. However, the complexity of these systems make them difficult to regulate and use.
After these separation steps, the organic layer is further separated into polypropylene wastes (called light organics), and separators and ebonite (called heavy organics). The light organics are then washed to remove traces of lead oxides, milled to small pieces, according to their future use, while the ebonite and separators are conveniently stored. Unless the breakage system is connected to the oven in a continuous process, the lead compounds and metallic parts are also stored until further processing.
Battery breaking methods differ from one another in process details and evolve as new technology becomes available. The suitability of each one for a given lead recovery plant depends on several specific factors such as local economy, quantity of raw materials as well as the demands of the smelting facility. Some examples of these systems are the Metaleurop, Bunker Hill, Gravita Technomech and MA Engineering, which can be understood in detail by consulting specialized references.
Nevertheless, every effort should be made to eliminate the use of manual battery breaking and the health and safety risks that are associated with this practice. If mechanical battery breaking equipment is unavailable, for whatever reason, the safest approach to prepare the battery for smelting would be the following: puncture and drain the electrolyte for the battery and treat it accordingly; remove the top of the battery complete with plates and separators using a circular saw and observing the correct use of guards and protective equipment; send the plates and grids with the top of the battery to the smelter; return the battery case to the manufacturer for reuse.
This section, and the other two sections in the lead reduction and lead refining processes, is not designed to describe or extensively list all possible sources of contamination that may occur in the lead recovery processes, since this is almost an impossible task. It is designed, instead, to itemize just a short and predictable list of common contamination sources and where to look when searching for them. Specific sources of contamination will have to be determined in the light of the process employed. Methods of contamination prevention will be treated in the environmental protection chapter. That stated, the common sources of environmental impacts in the battery breaking process are then:
(a) Spilling batteries – acid electrolyte and lead dust contamination source: battery spillage may be a very common source of environmental contamination as well as human health injuries since the electrolyte is not only a strongly corrosive solution but also a good carrier of soluble lead and lead particulates. Therefore, if this solution spills in an unprotected area, it may contaminate the soil or injure workers. Besides, after spilling on unprotected soil, the soil itself becomes a source of lead dust once the solution evaporates and the lead becomes incorporated into soil particles which may be blown by wind or raised by vehicle transit;
(b) Manual battery breaking – source of human health injury and environmental damage through heavy spillage and lead contaminated dust formation: manual breaking usually relies on primitive tools, poorly protected workers and no environmental protection whatsoever. The situation is even worst in the case of sealed batteries, which are not easily drained, increasing dramatically the risk of heavy spillage and damage to human health. Therefore, it should be avoided at all costs;
(c) Mechanical battery breaking – source of lead particulate: the process of breaking batteries through crushing on hammer mills may spread lead particulate. However, the fact that the mill is sealed and uses copious quantities of water the formation of such particulates is prevented.
(d) Hydraulic separations – contaminated water leakage: the hydraulic separations, both metallic from organic and heavy organics from light organics, are usually preformed inside sealed machines and with a closed water system. However, if any water leakage occurs, it will be heavily contaminated by lead compounds;
(e) Plastic and ebonite chips – contaminated wastes: ebonite scraps removed from the breaking process may pose a problem, since they are usually contaminated by levels as high as 5% (w/w) of lead. Therefore, it is important that the final traces of lead are removed by a second wash, preferably in an alkaline solution, followed by another rinse prior to further treatment or disposal.