Rotary / Al, Pb, Cu, precious metals / Scrap & other secondary, blister Cu / Oxidation and reaction with substrate.
Tilting Rotary Furnace[1] / Al, Pb / Scrap & other secondary / Minimizes salt & flux use.
Reverberatory / Al, Cu, Pb and others / Scrap & other secondary, black Cu
Isasmelt[2]/Ausmelt[3] / Cu, Pb / Intermediates, concs. & secondary materials. / Isasmelt and Ausmelt are same technology
QSL[4] / Pb / Concs. & sec. materials
Kivcet Flash Furnace[5] / Pb, Cu / Concs. & sec. materials
Blast Furnace and ISF / Pb, Pb/Zn, Cu, precious metals, high carbon ferro-Mg. / Concentrates, most secondary materials / For ferro-manganese production - only used together with energy recovery.
Outokumpu Flash Smelter[6] / Copper, nickel, lead / Concentrates
Kaldo Furnace[7] / Most non-ferrous metals, including Cu & Pb / Concentrates and secondary / Oxygen rich burner system
Table 1. Primary and Secondary Lead Furnace Options
Serious and urgent consideration must be given to either reconfiguring the present operation to accommodate lead concentrate or constructing a second smelter that is designed to switch from ULAB to lead concentrate and “visa versa”. Unfortunately, the number of feasible options for smelting both primary and secondary materials is limited and summarized in Table 1.
It is clear from the table that the current configuration at Hubei is not well suited to smelting primary and secondary materials. The reverberatory furnace is designed to treat secondary materials and despite the fact that the rotary furnace could be adapted or modified to process primary materials, it too small to be a viable option.
Alternatively, as the Company has considerable expertise in the field of electrolytic refining, consideration could be given to a hydrometallurgical process for the treatment of both primary and secondary materials. The PLACID process developed by Technicas Reunidas in Spain or a combination of the PLACID or the new PLINT[8] process in conjunction with pyrometallurgy might be more appropriate because it utilizes existing pyrometallurgical equipment thereby reducing the capital cost of any investment.
Fig.5 Isasmelt and Gas Supply Buildings
One important fact to bear in mind when considering the Isasmelt option is that the ULAB/lead concentrate recycling/smelting process is enhanced when the Isasmelt furnace is operated in tandem with a second furnace dedicated to grid metallics and by-products. The reason for this is that the Isasmelt furnace is ideal for producing antimony free lead bullion from a feedstock comprising of battery paste from the breaker. Given normal operating conditions any antimony in the battery paste will be retained in the furnace slag. As the company is producing Calcium lead alloys, and the demand is likely to increase, the more antimony free furnace lead bullion produced the quicker and cheaper will be the refining stage.
Accordingly, it is illogical to charge the Isasmelt with high Antimony furnace slag to recovery the metal content because the furnace will then be contaminated with Antimony and this may result in undesirable high Antimony bullion from the battery paste charges. Far better to charge the high Antimonial slags to a separate furnace and dedicate the Isasmelt to battery paste.
Professional advice has already been given to you suggesting that the most effective combination would be two Isasmelt furnaces, that is, one larger than the other with the largest being used to smelt either battery paste or lead concentrate. In preference, ILMC would recommend an Isasmelt/rotary combination for two reasons. Firstly, the company already has a relatively new rotary furnace that could be used, thereby reducing the capital cost of a plant upgrade substantially. It is a small furnace, but dedicated to melting grid metallics from the battery breaker and smelting and refining by-products, it might be large enough depending on the future throughput of the plant. Secondly, a rotary furnace will enable greater smelting flexibility for by-products and any other refining drosses and agglomerated baghouse fume. It should be noted that there is no real conflict in advice, as both combinations will work. Furthermore, both the ILMC and your professional consultant have independently recommended dry desulfurization in the furnace, demonstrating a clear convergence of opinion.
Ventilation and Dust Collection
There was little or no fume present in and around the plant, and although the baghouse system was not modern, each furnace had a separate extraction and ventilation sytem and everything seemed to be perfectly adequate. The only recommendation is to place covered collection bins under the drop out valves from the baghouses to prevent dust being blown out of the collection areas into the plant and the surrounding area. In addition, each of the covers on the collection bins should have a hole in the middle. This would permit a flexible tube to be attached to the end of the drop out valve and pass directly through the hole in the cover into the collection bin. In this way, the fume drops directly into the covered bin and none is lost to the wind (fig. 6).
Fig 6. Fume collection skip with cover and a flexible tube attached to the down pipe
Baghouse fume is mixed with the oxide paste from MA Breaker then charged to the furnace for lead recovery. As with all the methods of treating baghouse fume in a furnace, retention time is paramount. No mixing equipment was found and in the absence of a high temperature furnace to make fume bricks charging the fume mixed with oxide paste to a reverberatory furnace is the best option right now. Nevertheless, it is well know that fume most of the baghouse fume dust mixed with the oxide paste will simply separate from the paste in the furnace as the charge dries out and be “sucked” back into the baghouse before the reduction process has had time to act on the material. Consideration should therefore be given to some form of agglomeration furnace to fuse the fume dust into a solid mass that would have a long retention time in the furnace.
An agglomerator furnace is usually about 2 or 3 m square. The furnace can be easily fabricated locally and needs very little maintenance (Fig. 7). The baghouse fume dust is fed from a storage hopper via a rotary non return valve into a screw conveyor. Here a small quantity of soda ash is added from a second hopper, and then the mix is dropped onto a sloping hearth that has a gas or oil fired burner pointed towards and “playing” onto the hearth. The flame of the burner is set to a “lazy” yellow flame that has a wide flame front that covers the hearth area. Under the influence of the gentle heat from the burner, the fume dust will become molten, flow down the hearth and drip off the end of the sloping hearth into a collection pot. Sometimes limestone or iron oxide flux is added to the molten fume at this stage to mix it prior to smelting in the main furnace. The appearance and consistency of the agglomerated fume dust is similar to a hard brittle yellow plastic, but this metamorphism from dust to solid will increase the residence time in the furnace, improve lead recovery and reduce by-product re-circulation, and thereby costs.
Fig. 7 Agglomerator Furnace
Alternatively, if the company decides to install an oxygen supply to enrich the main lead furnace burners an agglomerator furnace similar to the one seen at the Doe Run Buick plant in Missouri, can also be contemplated. This furnace, designed and built by the Doe Run Company (Fig. 8), is a refractory lined dust agglomeration furnace with two oxygen enriched propane fired High Ram burners. One burner is located in the roof and the other is located in the end wall, and both are aimed directly at the feed pile. Unlike the agglomerator furnace outlined above and shown in figure 6, the furnace chamber gas temperature is maintained between 980°C and 1200°C, depending on the metallurgical components of the baghouse fume and dust.
The gas outlet duct from the furnace is refractory lined and is mounted in the center of the roof. This outlet duct is sloped at 60° to the process gas-cooling chamber, where it commingles with other process gases prior to the baghouse.The agglomerated slag is cast into a solid tapered 360 kilo block and then reduced in size (by cutting) prior to re-processing through the main lead furnace. The furnace “residence” time of the rock hard agglomerated leaded fume and dust substantially increases, and most of the lead is recovered with a pro-rata reduction in the re-circulating by-product load.
Fig. 8 Doe Run Agglomerator Furnace using Oxygen Enriched Propane Gas Burners
Refining and Casting
The refining and casting floor is labor intensive and employs the oldest technologies in the plant. The company plans to upgrade the whole of the area encompassing the refining and casting operations, and this will include the installation of automated casting machines. No final decisions have been made on the layout or the type of equipment.
The lead refining process followings traditional kettle refining methodologies to produce pure lead, and a range of lead alloys[9]. The manually operated equipment looks antiquated, but the Company achieves very high standards and has a Quality Control Laboratory with all the necessary instrumentation to analyze the lead ingots, and is also accredited with ISO 9001 for Quality Management.
The 25 K moulds for the ingots are arranged in the shape of a half “carousel” and filled on the floor of the building housing the Refining and Kettle floor. From a safety point of view, this arrangement is unsafe because employees are working above the molten metal and walk over and around the moulds during the casting operation as the surface of the molten lead is skimmed and the pouring spout is moved manually from one mould to the next.
The operators also use a pickaxe to “dig” ingots out of the moulds by swinging the tool at head height and bringing down the point of the pickaxe into the cast lead embedding it just enough to enable the ingot to be “levered” out of the mould. Assurances were given that this practice would cease when the automated casting machine was installed. Consideration should be given to terminating this procedure as soon as possible and a safe alternative method of removing the ingots from the moulds introduced.
Two possible options are:
- Side anchors – normally used for larger ingots and 1 MT blocks, but can be adapted for the 25 k moulds (Fig. 7)
Fig. 7 Side anchors for 1 MT lead blocks
- Screw anchors – either a heavy iron bolt with a “pulling eye” placed in the center of the mould or two smaller iron bolts placed at each end of the cast ingot. The ingot is removed from the mould by pulling on the “eye” with a chain and hoist and then after removing the lead ingot from the mould, the bolt is easily unscrewed from the ingot and used again. (Fig. 8)
Fig. 8 Screw Anchors
The surface quality of the ingots, apart form those with the pickaxe holes, was excellent and no inclusions were visible on any of the ingots inspected. This was quite surprising considering the simplicity of the casting operation and is a credit to the skill of the operators. The ingots stacks are bound in steel straps in 1 MT bundles and stored under cover on the site awaiting delivery to the customers.
Housekeeping
Apart from the baghouse fume dropping directly into the open storage bin beneath the rotary valves and the concrete immediately adjacent to the ULAB reception area the site was clean and tidy. The impression was not given that the Site had been cleaned specially for a visit by a representative from the ILMC, work procedures appeared to have been devised so that the minimum amount of waste and dust was generated and that any spillage or rejected material was taken to a designated place for disposal or recycling. Equipment was a clean and all unused tools stacked neatly in racks.
There were no boot cleaners at the office entrance, but as the plant was clean and not contaminated with leaded drosses, dust and charge materials, the “ritual” cleaning of the boots prior to entry into a “clean” area is probably deemed unnecessary. The inside of the office area was spotless, clean and tidy.
The only recommendation to make would be to clearly mark in yellow paint all the walkways around the plant and especially in the process areas. These designated walkways should always remain clear of any equipment or obstruction of any kind so that in the event of any emergency there is an unimpeded exit route for employees and ingress for the emergency services if they need access to the facility.
The Political and Legislative Situation for Secondary Lead Smelters in China
On August 3, 2002 the Chinese Ministry of Foreign Trade and Economic Cooperation, the Chinese General Administration for Customs and the State Environmental Protection Administration issued a joint statement announcing an import ban would come into force on August 15 for all the items listed in the fourth and the fifth lists of “Banned Imports.” The Lists were issued in accordance with the Regulations for the Administration of Imports and Exports, the Law on the Prevention and Control of Environmental Pollution by Solid Waste and the Notice on the Importation of Waste. Imports banned under the “Fourth List” include; slag, dross and other similar industrial waste; industrial ash and other waste materials containing lead, scrap batteries and so on.
The ban was enforced immediately and the next month on September 14, Taiwanese coast guards seized[10] four people and a fishing boat attempting to smuggle about 30 MT of ULAB from Taiwan to the Chinese mainland for a fee of nearly US$ 1,800. It is a certainty that the Chinese and Taiwanese Coast Guards and Environmental Agencies were aware of the activities of the smugglers and that such an illegal trade in ULAB is not uncommon. Indeed, according to reports from the Environmental Protection Agency[11] in Taiwan about 200 MT of ULAB are being smuggled annually to the mainland. Taiwan in a good source of ULAB with 6.6 million cars and 10.3 million motor scooters and it is estimated that there are about 50,000 MT of ULAB to be recycled annually, but the rate of collection and recovery at the one licensed recycler in Taiwan is only about 60%. It is also a certainty that the smuggled goods were destined for an unlicensed “backyard” recycler[12]. Such illegal activities might also have had a significant influence on the views of the Chinese government when they were considering whether to ban the import of ULAB.
Some Chinese officials I met at the Non Ferrous Metals Recycling Seminar in Ningbo mistakenly believe that the import ban on used lead acid batteries was passed into law in order to comply with the Basel Convention, of which China is a Party. How representative their misguided views are of the senior members of the legislature is impossible to determine on this visit, but it was disturbing that this was a viewpoint held by anyone in the government.
Whatever the reason for imposing the ban on the import of ULAB is unclear. Maybe the government thought that the batteries would be recycled in an environmentally unsound manner by the smaller recyclers or perhaps they thought that the ban was necessary to comply with an international convention. In any event, the reason is now somewhat academic. It is most unlikely that the government will lift the ban in the near future and so the Chinese secondary lead industry will be, and in some cases are already facing, a chronic shortage of ULAB at time when lead demand is at its highest and increasing.
For some years, a similar situation has existed in the Russian Federation and domestic prices for ULAB are now about US$ 100 per MT above the price paid on the international market. Understandably, the Russian secondary lead industry is in a very tight financial situation. The Chinese Secondary Lead Industry is not in the same position at present, but unless there is a clear strategy that will enable the recyclers to overcome the ULAB shortage and meet sales demands it is likely that many of the smaller businesses will be bankrupt is a couple of years.
The Management at the Jinyang Metallurgical Company is well aware of the future prospects for the supplies of domestically sourced ULAB and have a three-fold strategy: