Conservative technologies have been investigated in order to utilize n
atural and synthetic reactive polymers for selective metal removal, re
covery and reuse. Examples refer to the treatment of industrial wastes
containing silver, cadmium, mercury, chromium, iron and aluminum by d
ifferent innovative processes. A precipitation process is described, n
amely Metals Extraction by Xanthate Insolubilization and Chemical Oxid
ation (MEXICO), using agricultural raw materials to prepare starch or
cellulose xanthates as precipitating agents for metals. The process re
liability has been proven at pilot scale level (15 m(3)/d) by a demons
trative campaign treating continuously real chlor-alkali wastewaters f
or mercury removal and recovery. Results demonstrated Hg concentration
s in the filtered effluent in the range of 5-20 ppb, with an average r
emoval efficiency of 99.8%. The metal-xanthate sludge was then detoxif
ied by treating with NaClO solution at acidic pHs. Concentrated(> 10 g
/l) chlorocomplex Hg(II) solutions were obtained, to be directly recyc
led to the electrolytic cell. Other applications deal with the treatme
nt of segregated chromium in exhausted spent baths. The patented Ion E
xchange REcovery of CHROMium (IERECHROM) process utilizes a weak catio
n (carboxylic) ion exchange resin and allows for recovery and reuse of
90% of high purity (> 99%) chromium from other interfering metals suc
h as Fe and Al present in the spent tanning baths. A process for the t
reatment of tannery sludges has also been studied, particularly for po
ssible restoration of contaminated landfilling sites. The process is b
ased on the acid leaching of the sludges and on treating the leachate
by a weak base anion resin, selective to ferric species, coupled with
a strong cation resin (sulphonic) for the separation and recovery of c
hromium and aluminum.The economical evaluation of the conservative pro
cesses described is favorable, without taking into account the economi
c revenues from the recycling operation of the metals recovered and fr
om the minimized environmental impact related to these technologies. (
C) 1997 Elsevier Science Ltd.