Dust cadmium

Wear nitrile rubber gloves, laboratory coat, and eye protection. Avoid breathing dust. Cadmium compounds are not so toxic as to present serious disposal problems. The insoluble compounds can be mixed with wet sand, swept up, and treated as normal waste. The soluble salts can be mopped up with water, and a 10% aqueous solution of sodium metasilicate (Na2Si03-5H20) added until no further precipitation occurs. Adjust the pH to 11.0 with 2 M sulfuric acid. The solid is collected by filtration or by allowing the filtrate to evaporate in the fume hood. It is dried, packaged, and labeled for disposal in a secure landfill.14... 

SYNONYMS Colloidal cadmium, cadmium dust, cadmium fume. 

Cadmium is toxic and bioaccumulative in the environment (Department of the Environment 1984). In wastes, cadmium is nearly always present as (-1-2) oxidation state compounds rather than as native metal. As a dust, cadmium compounds (particularly CdO) are toxic by inhalation. Otherwise, the toxicity of cadmium compounds depends strongly on their solubility. The chloride, sulphate and nitrate are soluble and highly toxic whereas the carbonate, sulphide and hydroxide are less soluble. 

Production and Economic Aspects. Thallium is obtained commercially as a by-product in the roasting of zinc, copper, and lead ores. The thallium is collected in the flue dust in the form of oxide or sulfate with other by-product metals, eg, cadmium, indium, germanium, selenium, and tellurium. The thallium content of the flue dust is low and further enrichment steps are required. If the thallium compounds present are soluble, ie, as oxides or sulfates, direct leaching with water or dilute acid separates them from the other insoluble metals. Otherwise, the thallium compound is solubilized with oxidizing roasts, by sulfatization, or by treatment with alkaU. The thallium precipitates from these solutions as thaUium(I) chloride [7791 -12-0]. Electrolysis of the thaUium(I) sulfate [7446-18-6] solution affords thallium metal in high purity (5,6). The sulfate solution must be acidified with sulfuric acid to avoid cathodic separation of zinc and anodic deposition of thaUium(III) oxide [1314-32-5]. The metal deposited on the cathode is removed, kneaded into lumps, and dried. It is then compressed into blocks, melted under hydrogen, and cast into sticks. 

Copper sulfate, in small amounts, activates the zinc dust by forming zinc—copper couples. Arsenic(III) and antimony(TTT) oxides are used to remove cobalt and nickel they activate the zinc and form intermetaUic compounds such as CoAs (49). Antimony is less toxic than arsenic and its hydride, stibine, is less stable than arsine and does not form as readily. Hydrogen, formed in the purification tanks, may give these hydrides and venting and surveillance is mandatory. The reverse antimony procedure gives a good separation of cadmium and cobalt. 

Some of the melted ziac is fed to the ziac-dust unit where the molten ziac may be dropped from a cmcible through a small orifice (2.5 mm) to be atomized ia a blast of air. SoHdifted droplets are collected ia a chamber and screened to the proper size for purification and cadmium plant cementation. Frequently, coarse (+70 200 and fine (—70 fiva) fractions are required. 

Air pollution problems and labor costs have led to the closing of older pyrometaHurgical plants, and to increased electrolytic production. On a worldwide basis, 77% of total 2inc production in 1985 was by the electrolytic process (4). In electrolytic 2inc plants, the calcined material is dissolved in aqueous sulfuric acid, usually spent electrolyte from the electrolytic cells. Residual soHds are generally separated from the leach solution by decantation and the clarified solution is then treated with 2inc dust to remove cadmium and other impurities. 

Cadmium sulphide pigments, respirable dust, as Cd Caesium hydroxide... 

Cadmium and inorganic compounds of cadmium in air (X-ray fluorescence spectroscopy) Chromium and inorganic compounds of chromium m air (atomic absorption spectrometry) Chromium and inorganic compounds of chromium m air (X-ray fluorescence spectroscopy) General methods for sampling and gravimetnc analysis of respirable and mhalable dust Carbon disulphide in air... 

Fluorides and dust are emitted to the air from the fertilizer plant. All aspects of phosphate rock processing and finished product handling generate dust, from grinders and pulverizers, pneumatic conveyors, and screens. The mixer/reactors and dens produce fumes that contain silicon tetrafluoride and hydrogen fluoride. A sulfuric acid plant has two principal air emissions sulfur dioxide and acid mist. If pyrite ore is roasted, there will also be particulates in air emissions that may contain heavy metals such as cadmium, mercury, and lead. 

It is important to note that EAF dust is a hazardous waste because of its high concentrations of lead and cadmium. With 550,000 tons of EAF dust generated annually in the U.S., there is great potential to reduce the volume of this hazardous waste. The motivation for reducing this waste not only lies with the cost of air pollution controls, but with the cost for disposal. U.S. 

The primary hazardous components of EAF dust are zinc, lead, and cadmium nickel and chromium are present when stainless steels are manufactured. 

The composition of EAF dust can vary greatly, depending on scrap composition and furnace additives. EAF dust usually has a zinc content of more than 15%, with a range of 5 to 35%. Other metals present in EAF dust include lead (2-7%), cadmium (generally 0.1-0.2% but can be up to 2.5% where stainless steel cases of nickel-cadmium batteries are melted), chromium (up to 15%), and nickel (up to 4%). 

The principal constituents of the paniculate matter are lead/zinc and iron oxides, but oxides of metals such as arsenic, antimony, cadmium, copper, and mercury are also present, along with metallic sulfates. Dust from raw materials handling contains metals, mainly in sulfidic form, although chlorides, fluorides, and metals in other chemical forms may be present. Off-gases contain fine dust panicles and volatile impurities such as arsenic, fluorine, and mercury. 

The isolation of zinc, over 90% of which is from sulfide ores, depends on conventional physical concentration of the ore by sedimentation or flotation techniques. This is followed by roasting to produce the oxides the SO2 which is generated is used to produce sulfuric acid. The ZnO is then either treated electrolytically or smelted with coke. In the former case the zinc is leached from the crude ZnO with dil H2SO4, at which point cadmium is precipitated by the addition of zinc dust. The ZnS04 solution is then electrolysed and the metal deposited — in a state of 99.95% purity — on to aluminium cathodes. 

Cadmium Picrate. [C6H2(N02)30] 2Cd, mw 569.70, N 14.76%, yel powd which explds violently at 336—41°. Was obtained by heating one of its hydrates at 80—150°. Silberrad and Phillips (Ref 2) reported on the hepta- and pentahydrates, while Hopper (Ref 3) reported on the octahydrate. Sensitivity of the anhydr salt is 12" vs 14" for TNT, as detd with the PicArsn app using a 2kg wt. The value for the octahydrate is 35", making it less sensitive than BlkPdr dust... 

Butyl cellosolve, see 2-Butoxyethanol tert-Butyl chromate (as CrOj) n-Butyl glycidyl ether n-Butyl lactate Butyl mercaptan p-tert-Butyltoluene Cadmium, dust and salts (as Cd) Cadmium, fume (as Cd)... 

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