Waste minimization charges up recycling of spent lead-acid batteries BY PAUL B. AND ANTHONY L. T R O ~ ”

UBSTANTIAL STRIDES ARE BEING MADE TO MINIMIZE

waste generated from spent lead-acid battery recy- S cling. The Center for Hazardous Materials Research (Pittsburgh) recently investigated the potential for sec- ondary lead smelters to recover lead from battery cases and other materials found a t hazardous waste sites (W, “Technology,” April).

Primary and secondary lead smelters in the U.S. and Canada are p r m i n g subsmn- tial tons of lead wastes, and meeting regulato- ry safeguards, amrdmg to Hazen Research Inc (Golden, Colo.). Typical lead wastes in- clude contaminated soil, dross and dust byproducts ftom industrial lead consumers, tetraethyl lead residues, chemical manufac- turing byproducts, leaded glass, china clay waste, munitions residues and pigments.

The secondary lead industry also is de- veloping and installing systems to convert process inputs to products with minimum generation of liquid, solid and gaseous wlstes. The industry recently has made sub- stantial accomplishments that minimize waste generation during lead production from its “bread and butter” feedstock - spent lead-acid batteries.

Developments include: Installing gravity systems to separate

lead metallics and lead oxide-lead sulfate paste from battery casing components;

Recovering polypropylene chips from casings to be sold for reuse;

Using residual hard rubber (approxi- mately 13,000 Btu per pound) as hd 111 re- verberatory furnaces;

Employing a solvent extraction circuit to puri battery acid for reuse in new batter-

verted to ammonium bisulfite fertilizer, Leaching sulfur from battery paste to

produce sodium sulfite byproduct; and Replacing blast furnaces with single,

centrally located electric h a m , maximiz- ing lead, antimony and tin recovery, and permitting use of slag compositions with im-

ies, wi 2 most of the remaining sulfur con-

proved environmental stability. Secondary lead production. About

75 percent of 1992 U.S. lead production came from secondary sources. Primary and secondary production totaled approximately 1.3 million tons; secondary sources provided about 980,000 tons, including about 16,000 tons of lead in copper-based scrap. By com- parison, only about SO percent of 1980 U.S. lead production came from secondary

sources. Furthermore, about 85 percent of the nation’s recycled lead in 1992 was de- rived from spent lead-acid batteries, com- pared to about 70 percent in 1980. To meet this shift from primary to secondary lead, primary smelters have installed battery-pro- cessing facilities that dovetail with existing production operations. (Table 1 lists loca- tions, capacities and capabilities of U.S. sec- ondary lead plants; al l are smelters.)

Although most lead secondaries are recy- cled pyrometallurgically, traditional waste generation problems associated with this process have been solved by adding physical concentration and hydrometallurgical pro- cessiig steps. Until the early 1970s, batteries were broken by hand, typically by sawing off the top and dumping the contents. Casing components (primarily hard rubber, separa- tors and sulfuric acid electrolyte) were dis-

Table 1. Secondary lead smelters in the United States (as of June)

‘BF - blast furnace; REV - Revehratory; SRF - short rotary

1

34 HAZMAT WORLD - AUGUST 1993

S It of de-

3m- neet ead, pro-

oca- sec-

w- aste chis . i d ). ro- :lies q Off ,sing wm- diS-

ne)

Figure 1.1970s secondary lead plant in the United States

Waste

Carbon, Waste Flux,

Dross sulfur dioxide

son lead to refining

Flux, Vent gas Carbon

Figure 2. Battery breaking and physical con- centration of components

BaHeries Water

................

Crusher Q ........ ....................

Water

1 Ebonite. seoaraton

Figure 3.1980s secondary lead plant in the

Polypropylene Waste

United States

Sodium carbonate . .

Sodium sulfate Flux,

Dross Carbon, Vent gas

son lead to refining

Vent gas Flux,

Carbon

Figure 4.1990s secondary lead plant in the

Sulfuric acid Polypropylene

United States

Sodium sulfate Rubber and separators

Vent gas

son lead to refining

Vent gas

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Recycling batteries - -

carded in landfills. Selective reduction of lead components in a reverberatory furnace produced relatively pure soft lead for the re- finery, as well as a lead oxide-rich slag con- - taining antimony, tin and arsenic alloying el- ements. Sulfur was vented as sulfur dioxide (SOz) after baghouse filtration removed dust, which was returned to the reverberato- ry furnace. The reverberatory slag then was reduced further in a blast furnace to produce hard-lead bullion and discard slag. Altema- t idy, the d d batteries were smelted di- rectly in a blast furnace to pro-

percent. This leaching step eliminates prob- lems related to SO, emissions and matte generation during subsequent reverb smelt- ing or blast furnace operation. An alternative to leaching sulfur from battery paste is to convert SO2 generated during smelting to ammonium bisulfite fertilizer.

Using an electric furnace rather than a blast furnace to treat reverb slag was com- merualized in 1988 by RSR Corp. (Dallas). Separators recovered from physical con- centration contain about 60 percent silica, 15

percent calcium oxide and barium oxide, 15 percent carbon, 10 percent aluminum oxide, and 0.1 percent chloride. This waste is fluxed during smelling, exiting the blast or e l d c furnace as discard slag (Figure 4). A higher slag temperature (about 1,425 de- grees Celsius, or 2,600 degrees Fahrenheit) immediately before tapping permits using slag compositions with improved environ- mental stability. The higher slag tapping temperature also reduces flux consumption, decreasing slag volume by about one-third,

and incxeasing recovery of lead, anti- due- bullion, matte and slag(see mony and,, particularly, tin. Bag- Figure 1). house dust IS returned continuously

During the 1980s, the sec- to the reverberatory furnace. ondary lead indusay and its sup- During the first half of 1993, sec- pliers developed and installed ef- ondary smelters purchased unbroken ficient gravity systems to physi- batteries for about 1 3 cents per cally separate spent automobile pound of lead, f.0.b. the smelter. batteries into manageable hac-, Soft lead (free of alloying mons (see Figure 2; components elements) produced by sec- in a typical spent auto battery are ondary smelters typically suIllltl;uized in Table 2; analyses sold for 2 1 to 25 cents per of grid arid paste fi-actions appear pound, an exceptionally in Table 3). Polypropylene re- low price when compared placed hard rubber as the prhmy to lead pricing (in constant material in battery casings. dollars) over the past quar- Washed polypropylene chips re- ter century. H a r d lead covered from battery breaking -- containing greater than 3 and concentration operations percent antimony and less sold (to recyclers) for about 35 than 0.05 percent tin am- cents per pound in 1990. BY ___._.._ !eparat!.E.-.P!!o!! mands about a 1 cent per

Dound lead oremiurn. Twical cash Sulfuric acid - 10 PO 1992, when supply from sec- ~ -.. ondary polypropylene sources caught up with demand, the price d e d to a b u t 15 cents per pound.

Hard rubber from older batteries Stiu is recoveTed for use as fuel in the reverberatory furnace. Oxygen is added during furnace charging or in the afterburner to consume the hard rubber's 2 5 to 3 5 percent volatile content These improvements, attained by physically concentrating spent solid battery componem, are mm"d ' inFigure4.

Scseening and sink-float treatment effi- ciently separate and concentrate sulfur-rich battery paste, further improving the process. For example, East Penn Manufacturing Co. (Lyon Station, Pa.; Table 1) uses solvent ex- traction to purify sulfuric acid byproduct from battery breaking for reuse in new bat- teries. Sulfur hed as lead &te in battery paste also can be removed before smelting the paste, producing salt cake byproduct rather than SO2 offgas. Sulfate is leached h m the paste with soda ash, yielding sulfur as marketable sodium &te.

Pre-leaching feedstock removes and re- covers sulfur as sodium sulfate before melt- ing (Reaction I), decreasing the paste's sulfur content &om about 5 percent to less than 0.5

Table 3. Typical grid and paste analyses

Reaction 1. -04 (paste) + Na2C03 (aqueous) + PbC03 (paste) + Na+04 (aqueous)

and imortized broduction 'costs for U.S. secondary lead producem are 10 to 12 cents per pound and 13 to 15 cents per pound of lead, respectively, excluding lead purchase costs. Therefore, total cash cost for the most efficient producers was about 22 cents per pound of lead produced (or equiva- lent to the cash received for lead sales). Thus, it is not surprising that several smelters shut down operations during 1992.

Hydrometallurgical research. over the past decade considerable research and testing have focused on replacing lead smelting with leach-electrowin processes. Initial physical treatment and soda ash leaching operations have similar conven- tional pyrometallurgical (see Figure 4) and proposed hydrometallurgical processes. Be- fore leaching and electrowinning, batteries are crushed and lead is concentrated by physical means (see Figure 2). Battery paste is ieached IO rejtxt S&K.

There are at least three leach-electrowin processes, all of which have been tested on a pilot-plant scale by RSR, B.U.S. Engitec

tree City, Ga.): RSR's process decomposes lead carbon-

ate-lead oxide leach residue to lead oxide, which then is leached with f ludc ic acid (re- turn electrolyte) lead is electrowon h m the

(Miho, Italy) and M A Industries (Peach-

solution u&g lead oxideaated graphite an- odes, and grids are treated pymmetallurgidy.

36 HAZMAT WORLD - AUGUST ism3

1

r I .i

I1 a

’C 1-

1-

e, e- le

Y. 1-

B.U.S. Engitec uses fluoboric acid to elec- trowin lead from battev paste, and an iron fluobo- rate system electrowins lead from the grid.

M.A. Industries em- ploys a titanium additive in its fluoboric acid leach- ing media. The additive acts as a redox pair that re- acts with and dissolves lead and lead oxide. This lead, along with lead leached from lead carbon- ate, is recovered by elec-

In all these processes, spent tankhouse elec- trolyte returns to leach lead from incoming bat- terv-derived feedstock.

trowinning.

Physical separation and conceiwation ofspent hd-acid battery components facilitates recycling

These electrowinning processes have not found commercial application in the sec- ondary lead industry, principally because the smelting processes they were intended to re- place have been improved. The most eco- nomic and optimum process for batteries ap- pears to be a combined application of physi- cal concentration, leaching and smelting.

Major consumers require lead as elemen- tal metal. Demand for hydrometallurgical technologies, therefore, likely will focus on electrowinning to produce metal, feedstock modification to accept new raw materials, and bleed impurity treatment to meet increasing economic and environmental demands.

The combination of physical, hydromed- lurgical and pyrometallurgical processes sig-

nificantly has reduced waste generation from recycling spent lead-acid batteries. Gravity processing, hydrometallurgy and pyrometa- lurgy work together to provide leading-edge innovation for profitable recycling. T

Pad B. Queneau is a p m p a l metnllzcl-gical engineer, and Anthony L. Eoiirinan is a py+-t enginew at H a m Research hc. (Gohz, Cofo.).

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