Preliminary Treatability Studies

Initially, studies were done on the battery casings and soils to determine if physical methods could be used to concentrate the contaminants and reduce the volume of material that had to be treated. Since lead compounds have a relatively high density, gravity separation was a logical choice. The fineness of the soils (<37 (im) suggested that a Bartles-Mosely vanner be used for the gravity separation since it is the only gravity separator that has had any success on <37 fxm materials. The soils contained a high percentage of fines (approximately 15% was <2 |tm) that the vanner could not separate, so there was little or no upgrading. Next, a series of flotation tests were done using a xanthate collector, mercaptobenzothiazole, and an amine. The best en-

Table 6 Analysis of Battery Sludge

Element

ppm

Element

%

Ag

6

Al

0.52

As

122

Ca

2.8

Ba

245

Fe

1.3

Cd

6

Mg

0.72

Cr

24

K

0.09

Hg

ND

Na

0.02

Pb

52,000

C

21.2

Sb

858

s

0.22

Se

< 5

Si

ND

ND = not determined.

ND = not determined.

richment ratio was 2:1 at a recovery of 20% Pb. Feed grades were reduced, on average, from

0.7. to 0.5% in one pass. Although this test work showed that there was some selectivity toward the lead minerals present, better reduction of the feed grade would be necessary to consider flotation as a removal method for the lead. Tests using carrier flotation or an air-sparged hydrocyclone were also applied but showed no improvement. A series of hydrometallurgical approaches were investigated next.

Preliminary tests on the casings included a water soak. The battery chips were first broken into minus 3/8-in. pieces and then soaked-stirred in water for 4 days. Various chemical additions were made to the water along with more aggressive scrubbing methods. An ultrasonic cleaner was used with various surfactants, detergents, and known lead solubilizers [disodium ethylenediamine tetraacetate (EDTA), ammonium acetate, sodium citrate, acetic acid, H2SiF6, and HN03]. One approach consisted of soaking the material in EDTA for 3 days. After this treatment, the cleaned battery casings passed the EPA EP toxicity test with <5 ppm Pb in the extract and also met the standard of <500 ppm Pb in the residue. However, the chips disintegrated badly, making solid-liquid separation very difficult, and lead removal from the spent EDTA was not achieved. Based on previous scrap-battery research, it was known that converting the sulfates to carbonates [8] and reducing the dioxides to oxides would form readily soluble compounds of all lead except the metallic Pb, which is slightly acid-soluble when finely divided [9], An acid wash could then be used to remove the lead. Size reduction would help to expose the lead trapped in the cracks and fissures of the casings. The larger pieces of metallic lead would be removed by a gravity separation method, and the finely divided (minus 18 mesh and smaller) pieces would be soluble in the time frame used for acid leaching.

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