Cyanide speciation at four gold leach operations undergoing remediation
Craig A Johnson1, David J Grimes, Reinhard W Leinz
1U.S. Geological Survey, Box 25046, MS 963, Denver, Colorado 80225, USA. cjohnso@usgs.gov
Environmental Science & Technology
|March 21, 2008
Summary
Cobalt, not previously recognized, forms stable complexes with cyanide in gold mine effluents. These cobalt-cyanide complexes contribute significantly to cyanide persistence, requiring further study in mining waste management.
Area of Science:
- Environmental Chemistry
- Geochemistry
- Mining Engineering
Background:
- Cyanide is widely used in gold extraction.
- Persistent cyanide species in mining effluents pose environmental risks.
- Existing research often overlooks specific metal-cyanide complexes.
Purpose of the Study:
- Identify persistent cyanide species in gold leach effluents.
- Investigate the role of metal-cyanide complexes in cyanide persistence.
- Determine the prevalence and impact of cobalt-cyanide complexes.
Main Methods:
- Analysis of 81 effluents from four gold leach operations.
- Measurement of total cyanide and weak acid-dissociable (WAD) cyanide.
- Quantification of metals forming stable cyanocomplexes, including cobalt and iron.
Main Results:
- Total cyanide exceeded WAD cyanide, indicating strong cyanometallic complexes.
- Cobalt concentrations were sufficient to form stable cobalt-cyanide complexes.
- Cobalt-cyanide complexes were identified across multiple gold mining operations.
- Photodissociation experiments showed cobalt's capacity to retain liberated cyanide.
Conclusions:
- Cobalt-cyanide complexes are a significant, previously unrecognized source of cyanide persistence in gold mining wastes.
- The abundance of cobalt in ores is not necessarily high for complex formation.
- Further research is needed on the behavior and management of cobalt-cyanide complexes in mining effluents.
Related Concept Videos
01:27Microbial Leaching
Microbial leaching, also known as bioleaching, is an environmentally favorable method for extracting metals from low-grade ores using specific microorganisms. This biotechnological approach is particularly valuable for mining operations targeting copper, gold, and uranium, where traditional extraction methods may be economically or environmentally impractical.Copper Leaching and Microbial CatalysisIn copper bioleaching, crushed ore is arranged into heaps and irrigated with a dilute sulfuric...
01:17Precipitation and Co-precipitation
Precipitation and coprecipitation methods can be used to separate a mixture of ions in a solution. In qualitative inorganic analysis, ions that form sparingly soluble precipitates with the same reagent are separated based on the differences in solubility products. For example, consider the separation of Cu(II) and Fe(II) ions by precipitation as insoluble sulfides. First, copper(II) sulfide is precipitated by the addition of acidic H2S, where the dissociation of H2S is suppressed. Adding H2S...
00:56Extraction: Advanced Methods
Metal ions can be separated from one another by complexation with organic ligands–the chelating agent– to form uncharged chelates. Here, the chelating agent must contain hydrophobic groups and behave as a weak acid, losing a proton to bind with the metal. Since most organic ligands used in this process are insoluble or undergo oxidation in the aqueous phase, the chelating agent is initially added to the organic phase and extracted into the aqueous phase. The metal-ligand complex is formed in...
03:45Formation of Complex Ions
A type of Lewis acid-base chemistry involves the formation of a complex ion (or a coordination complex) comprising a central atom, typically a transition metal cation, surrounded by ions or molecules called ligands. These ligands can be neutral molecules like H2O or NH3, or ions such as CN− or OH−. Often, the ligands act as Lewis bases, donating a pair of electrons to the central atom. These types of Lewis acid-base reactions are examples of a broad subdiscipline called coordination...
01:19Masking and Demasking Agents
EDTA titrations may necessitate masking and demasking agents to temporarily protect a particular metal ion in a mixture from the EDTA reaction. These agents facilitate the sequential analysis of the metal ions by forming stable complexes with some—but not all—metal ions during certain steps.
There are many masking agents, such as cyanide, fluoride, triethanolamine, thiourea, and 2,3-bis(sulfanyl)propan-1-ol (formerly 2,3-dimercapto-1-propanol), with the masking agent chosen based on the metal...
There are many masking agents, such as cyanide, fluoride, triethanolamine, thiourea, and 2,3-bis(sulfanyl)propan-1-ol (formerly 2,3-dimercapto-1-propanol), with the masking agent chosen based on the metal...
01:25Microbial Bioremediation of Uranium
Microorganisms play a critical role in the transformation and immobilization of uranium in contaminated environments through four main pathways: bioreduction, biosorption, bioaccumulation, and biomineralization. These mechanisms reduce uranium’s toxicity and prevent its migration through groundwater systems, offering sustainable approaches for in situ bioremediation.Bioreduction of UraniumBioreduction is driven by anaerobic bacteria such as certain strains of Geobacter and Shewanella, which use...