Environmental Engineering Reference
In-Depth Information
consideration and contributor to process costs and metal(s) recovery in
a concentrated form. A successful desorption process must restore the
sorbent close to its initial properties for ef ective reuse. Desorption can
be improved by gaining insight into the metal sorption mechanism. In
most of the arsenic sorption studies discussed earlier, desorption/regen-
eration was not discussed. Very few desorption studies are detailed in lit-
erature. Furthermore, once arsenic is recovered in the concentrated form,
the problem of how to dispose of this concentrated arsenic product must
be addressed. h is is a dii cult task. Few attempts have been made in the
literature to address the handling of concentrated arsenic wastes. Various
disposal options and their advantages and disadvantages were reviewed
[133]. h e methods frequently used for other metals and organics include
combustion or recovery and purii cation for resale. h ese options are not
feasible for arsenic due to the following reasons:
• Incineration is not practically feasible because arsenic oxides
are volatile and can easily escape.
• Recovery and purii cation of arsenic is not cost ef ective
because arsenic has limited markets.
3.2.1 Cost Evaluation
h e cost of arsenic removal adsorbents developed from waste materi-
als seldom appears in the literature. h e cost of individual adsorbents
depends on local availability, processing required and treatment condi-
tions. h ese are not broadly and thoroughly discussed in any paper any-
where in the literature. Costs will vary when the adsorbents are made in
(and for) developed countries, developing countries or underdeveloped
countries. Numerous commercially available activated carbons have been
used for arsenic adsorption, both as-received and at er chemical modii ca-
tions. However, chemical modii cation costs are seldom mentioned in the
research reports. Furthermore, no consistency exists in the data presented.
Most papers describe only batch experiments but not i xed-bed stud-
ies. Batch equilibrium adsorption isotherms cannot simulate or predict
dynamic performances directly due to the following limitations:
•
Isotherms are equilibrium tests so the time restrictions are
not considered.
•
Isotherms are based on carbon exhaustion-granular systems.
•
Long-term chemical and biological ef ects are not evident.
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