New Generation Material for the Removal of Arsenic from Water - Advanced Materials for Agriculture, Food and Environmental Safety - page 71

by natural zeolites, volcanic stone, cretaceous powder CACMM and
clinoptilolite-containing rocks was studied. h e content of the zeolitic
phases was: 55% clinoptilolite + 35% erionite in ZMA (Maxican, Sonora),
40% clinoptilolite + 30% mordenite in ZME (Maxican, Oaxaca) and 55%
clinoptilolite + 30% mordenite in ZH [90, 91]. h e adsorption of As(V)
from drinking water by an aluminum-loaded Shirasu-zeolite (Al-SZP1)
was slightly dependent on the initial pH over a wide range (3-10) [92].
h e Al-SZP1's ability to adsorb As(V) was equivalent to that of activated
alumina.
Competition arsenite, chloride, nitrate, sulphate, chromate, and acetate
ions had little ef ect, but phosphate greatly interfered with the adsorption.
A ligand-exchange mechanism between As(V) ions and surface hydroxide
groups on Al-SZP1 was presumed. h e adsorbed As(V) ions were deso-
rbed by 40 mM aqueous NaOH. An iron-conditioned zeolite was prepared
and used for arsenic removal from groundwater at pH 7.8 and temperature
145

° C [93]; other parameters are shown in Table 3.6.

3.1.5.9 Oxides

3.1.5.9.1 Manganese Dioxide
Manganese oxide minerals have important environmental chemistry
uses. Arsenic removal from drinking water by monocomponent i xed-bed
adsorption of phosphate and arsenate using two natural manganese oxides
was investigated [94, 95].

3.1.5.9.2 Activated Alumina
Activated alumina (AA) prepared by thermal dehydration of aluminium
hydroxide has a high surface area and a distribution of both macro- and
microspores. h e United Nations Environment Programme (UNEP)
agency classii ed AA adsorption among the best available technologies for
As removal from water. Arsenic(V) sorption occurs best mostly between
pH 6.0 and 8.0, where AA surfaces are positively charged. h e adsorption
of As(III) is strongly pH dependent and it exhibits a high ai nity towards
AA at pH 7.6 [96]. Arsenites from water were removed with AA and
iron oxide-impregnated AA [97]. h e ef ect of adsorbent dose, pH, and
contact time were investigated. h e removal of As(III) was strongly pH
dependent. h e adsorption capacity of iron oxide-impregnated AA was
12 mg/g. Precipitated Fe(OH)3 on the surface of activated Al 2 O 3 supports
was used. h e Fe content of the AA was 0.31% m/m (56.1 mmol/g) hav-
ing pHzpc = 6.9. h e total capacity was 0.12 mmol/g. h e adsorbent can
be used for binding both anions and cations by varying the pH. If pHeq <
pHzpc, anions are sorbed on the Fe(OH) 3 /Al 2 O 3 surface through surface