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Quantitative and Qualitative Extraction and Determination of Cyanide in Soils and Sediments
Poster Presentation
Prepared by W. Lipps
OI Analytical, 151 Graham Road, College Station, Texas, 77845
Contact Information: william.lipps@xyleminc.com; 979-690-5230
ABSTRACT
The toxicity and mobility of cyanide in soil is governed by its chemical form. Simple cyanide, or the cyanide ion (CN-), can be weakly adsorbed onto soil particles at pH >9.2. Weak metal-cyanide complexes ([M(CN)4]-2 and strong metal – cyanide complexes ([M(CN)6]-3 or [M(CN)6]-3) have an affinity for metal oxides and organic matter that decreases with increasing pH, however, other salts in solution tend to inhibit adsorption. Simple cyanide, weak metal-cyanide complexes, and strong-metal cyanide complexes are readily soluble in water. Metal – Metal cyanide complexes, such as Prussian Blue (Fe4[Fe(CN)6)3 ), are insoluble in water and are the most common forms of cyanide found in sediment and soil.
A common practice for the extraction of cyanide in soil and sediment is acid distillation. This approach is valid for all cyanide forms except the metal-metal cyanide complexes that are most likely to be present. The quality control practice of spiking a soil sample with simple cyanides, or strong metal-cyanide complexes to validate acid distillation is misleading because these cyanide complexes are readily soluble. Acid distillation of cyanide in soil results in low and irreproducible recoveries for the metal-metal cyanide complexes most likely to be present. Acid distillation of cyanide in soil is ineffective and does not accurately measure “total” cyanide nor does it estimate cyanide toxicity.
This will present an extraction and analysis scheme that selectively extracts and determines the various forms of cyanide that could be present in a soil or sediment sample. Analytical results demonstrating differentiation of potentially toxic simple and weak metal-cyanide complexes as well as non toxic cyanides, strong metal-cyanide, and metal-metal cyanide complexes will be reported.
(Related Session: EPA Approval of Innovative Approaches to Monitoring)
Poster Presentation
Prepared by W. Lipps
OI Analytical, 151 Graham Road, College Station, Texas, 77845
Contact Information: william.lipps@xyleminc.com; 979-690-5230
ABSTRACT
The toxicity and mobility of cyanide in soil is governed by its chemical form. Simple cyanide, or the cyanide ion (CN-), can be weakly adsorbed onto soil particles at pH >9.2. Weak metal-cyanide complexes ([M(CN)4]-2 and strong metal – cyanide complexes ([M(CN)6]-3 or [M(CN)6]-3) have an affinity for metal oxides and organic matter that decreases with increasing pH, however, other salts in solution tend to inhibit adsorption. Simple cyanide, weak metal-cyanide complexes, and strong-metal cyanide complexes are readily soluble in water. Metal – Metal cyanide complexes, such as Prussian Blue (Fe4[Fe(CN)6)3 ), are insoluble in water and are the most common forms of cyanide found in sediment and soil.
A common practice for the extraction of cyanide in soil and sediment is acid distillation. This approach is valid for all cyanide forms except the metal-metal cyanide complexes that are most likely to be present. The quality control practice of spiking a soil sample with simple cyanides, or strong metal-cyanide complexes to validate acid distillation is misleading because these cyanide complexes are readily soluble. Acid distillation of cyanide in soil results in low and irreproducible recoveries for the metal-metal cyanide complexes most likely to be present. Acid distillation of cyanide in soil is ineffective and does not accurately measure “total” cyanide nor does it estimate cyanide toxicity.
This will present an extraction and analysis scheme that selectively extracts and determines the various forms of cyanide that could be present in a soil or sediment sample. Analytical results demonstrating differentiation of potentially toxic simple and weak metal-cyanide complexes as well as non toxic cyanides, strong metal-cyanide, and metal-metal cyanide complexes will be reported.
(Related Session: EPA Approval of Innovative Approaches to Monitoring)