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NEWS ARCHIVES
Initial inspection of cyanide waste
inventory
Decontamination of empty canisters with
NaOCl (sodium hypochlorite)
Repackaging canister contents into polythene
bags
Decontaminating the storage building with
sodium hypochlorite (repackaged cyanide on left)
Adding cyanide/cellulose discs to the
chemical oxidising mixture
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Evaluation
of Plan of Action for the Safe Disposal of Hazardous Waste
Material Containing Cyanide
Dr. Brace Boyden, a
chemical engineering consultant from Sydney, was recommended by the
Pacific Basin Consortium for Hazardous Waste Research and Management
to the World Health Organization (Manila Office) to assess the
condition of the Suva, Fiji storage site and develop a Plan of
Action for safely disposing of the old stock of hydrogen cyanide
discoid. The project was undertaken in cooperation with the
Government of Fiji and the South Pacific Office of WHO.
In 2000, the
Fijian Ministry of Health (MOH) approached Dr Donald Sharp,
Environmental Engineer for the WHO, in Suva regarding possible help
with the safe removal and disposal of the now aged stock of
cyanide. Cyanide had been used for a number of years in Fiji
for the fumigation of ships to control unwanted rodents and
pests. This practice was discontinued about 16 years ago, but
unused stock remained in a storage facility in
Suva.
The cyanide
(sodium cyanide impregnated cardboard discs, approximately 150 mm in
diameter and 1 mm thick) was stored in 500 g steel canisters in a
ventilated shed on MOH premises in Suva. The length of storage
and local environmental conditions had more than likely corroded the
canisters, thus making entry into the storage facility unsafe (i.e.
hazardous) without proper protective clothing and gas
mask.
It was
determined after the initial inspection that disposal via the local
cement kiln could offer the safest alternative. However,
containment of the cyanide waste was necessary as a first step to
enable its safe handling. The containment process was
initiated by opening the corroded steel canisters and repackaging
their individual contents into polythene bags and sealing the
bags. The bags were in turn placed in 10, 20 L plastic drums
and the drums sealed with a gas tight lid. Approximately 50%
of the canisters (20 kg) still contained fully active (ie high NaCN
content) cellulose discs. The remaining canisters contained
varying degrees of degraded discs; in some only black powder
(carbon?) remained.
Once the
cyanide had been properly contained, the storage building and all
its contents, including the empty steel canisters, were
decontaminated with a solution of sodium hypochlorite to oxidise any
residual sodium cyanide to less hazardous compounds (e.g. water
vapour, carbon dioxide, sodium chloride, and oxides of
nitrogen).
The local cement kiln operator
(Basic Industries Limited) was contacted regarding the possible use
of the kiln for incineration of the cyanide. After extended
negotiation over a three-day period, involving letters from the WHO,
the WHO consultant and the Fijian Ministry of Health, Basic
Industries Limited declined to allow the disposal of the cyanide
waste in their kiln. An alternative plan was therefore
actioned in which the cyanide waste was unpackaged and mixed with a
solution of calcium hypochlorite (CaOCl) at high pH (>9.5) in
44-gallon drums. Calcium hypochlorite was added in steps and
in stoichiometric excess (the reaction is highly exothermic) and
allowed to continue over night to ensure complete mineralisation of
the cyanide.
The following day (about 18 hours
later) additional CaOCl was added over the course of four hours to
affect the oxidation of any residual cyanide. The pH of the
mixture was subsequently decreased to between pH 7.2 and 7.4 with
sodium bisulphate. The cellulose discs were then removed, hand
dewatered and bagged into 10, 40 L rubbish bags. The discs
were now safe for disposed in a municipal landfill and the Director
of Health Services was contacted to gain permission for this.
The residual chemical solution, now a mixture of salts at near
neutral pH 7, was absorbed into sand and landfilled.
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