Feasibility and cost of creating an iron-phosphate coating on pyrrhotite to prevent oxidation

Georgopoulou, Z. J.; Fytas, Kostas; Soto, H.; Evangelou, Bill P.

doi:10.1007/s002540050078

Cited by 33 publications

(17 citation statements)

References 14 publications

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“…This further reduction with phosphate is due to neutralization of acid and precipitation of FePO 4 which removes Fe +3 oxidant, avoids production of Lewis acidity upon neutralization and, ideally, coats and armors metal sulfide surfaces. Conditions for coating formation probably require Fe +3 iron at the surface of the mineral, adequate soluble phosphate and the correct pH (Evangelou, 1996). If the pH is too low (i.e., <3) soluble phosphate treatment is ineffective because precipitation of FePO 4 is reduced and existing FePO 4 precipitates are destabilized.…”

Section: Discussionmentioning

confidence: 99%

“…These have included use of silica (Fytas and Bousquet, 2002), permanganate (developed by DuPont), or phosphate (Evangelou, 1995;Georgopoulou et al, 1996;Nyavor and Egiebor, 1995) to create armoring layers on metal sulfide surfaces. Achieving efficient armoring with sufficient longevity appears to be the major challenge.…”

Section: Control Of Abiotic Metal Sulfide Oxidationmentioning

confidence: 99%

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Toward Source Control of Acid Rock Drainage

Olson¹,

Clark²,

Mudder³

et al. 2006

JASMR

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Abstract. Source control of acid rock drainage (ARD) requires consideration of both biological and abiotic mechanisms of metal sulfide oxidation. A promising approach is to couple a biocide with phosphate for application to sulfidic waste materials. This approach aims to 1) inhibit or kill with thiocyanate (SCN) the iron-oxidizing acidophilic microorganisms that accelerate sulfide oxidation and 2) precipitate FePO 4 and AlPO 4 , thereby removing ferric ion oxidant and Lewis acidity, and, in the process, armoring the surface of pyrite to retard its abiotic oxidation. Thiocyanate effectively reduces sulfide biooxidation if it is applied efficiently and is not washed out of the system by rainfall or adsorbed to the rock. Several sources of phosphate including phosphate rock, waste material and agricultural products were characterized and tested in combination with SCN for their ability to retard oxidation of sulfidic waste rock. Waste rock sources include samples from base metal and precious metal mines and a coal mine. The acid neutralizing capacities (ANC) of different sources of phosphate were compared and evaluated using an artificial ARD solution which included iron and aluminum sulfates. Thiocyanate alone in laboratory tests sharply reduced ARD production, approaching the abiotic rate of sulfide oxidation. Whether thiocyanate plus phosphate further reduced ARD production depended on the mineral sulfide composition of the waste rock and the parameter measured. The abiotic sulfide oxidation rate of sphalerite-containing waste rock was reduced with phosphate treatment, most likely by removal of residual ferric iron from leach solutions. Phosphate did not further reduce abiotic sulfide oxidation rates with a pyritic waste rock, but did significantly reduce the soluble iron and other metal content of leachates.The combined thiocyanate plus phosphate treatment minimized biooxidation, removed ferric ion oxidant, and restricted formation of Lewis acidity but has not shown evidence of armoring pyrite. The laboratory test work guided the set up and operation of a 3000 t field test. ARD production was reduced over 50% in the first season with combined thiocyanate and phosphate treatment. However, washout of thiocyanate and its adsorption to rock reduced its concentrations in leachates to near zero in the second year of the test, greatly reducing the effectiveness of chemical treatment. Water soluble forms of thiocyanate (NaSCN) are best used to reduce ARD in situations where rainfall infiltration is low. The development of slow-or controlled-release thiocyanate products combined with phosphates would be beneficial.

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Section: Discussionmentioning

confidence: 99%

Section: Control Of Abiotic Metal Sulfide Oxidationmentioning

confidence: 99%

Toward Source Control of Acid Rock Drainage

Olson¹,

Clark²,

Mudder³

et al. 2006

JASMR

View full text Add to dashboard Cite

show abstract

“…In the former category are techniques such as coating of sulfidic materials with non-reactive compounds such as metal phosphates (Evangelou 1994;Georgopoulou et al 1996) or silica (Zhang and Evangelou 1998). A similar strategy involves adding solutions that inhibit activity of iron-oxidizing bacteria that catalyze AMD production at low pH (Parisi et al 1994).…”

Section: Introductionmentioning

confidence: 99%

Alkaline Injection of Concentrated Sodium Hydroxide Solution into an Acidic Surface Mine Spoil Aquifer

2008

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A series of NaOH solution injection experiments were performed as trials for in situ remediation of an acid-producing surface-mine spoil. Both 20 and 50% (w/w) concentrated NaOH solutions were employed. While the spoil immediately down-gradient of the injection wells was neutralized, only about 23% of the introduced Na was recovered at the spring discharge in 3 years of post-injection monitoring. This rate of transport was far slower than the estimated advection rates in the aquifer, indicating that substantial retardation of both Na and the associated alkalinity occurred. This retardation is ascribed to: precipitation of alkaline-earth carbonate hydroxide minerals, as well as metal hydroxide precipitates, consuming injected alkalinity; and reduction of hydraulic conductivity in the peralkaline (pH [ 13) ''plume'' region due to plugging by reaction products. It is likely that Na and alkalinity will continue to leak from this plume region for many years, but at too slow a rate to neutralize AMD at current concentrations. Future injection efforts of this type may be feasible but should use lower concentrations and should be focused further down-gradient, in closer proximity to the springs, where ground water velocities are higher.

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“…The most common solution suggests adding limestone to the acid waste tailings, since increasing the pH the weathering of iron sulphides slow down. Other interesting suggestion is to cover the pyrite surface (10-12), or pyrrothite outer (13), by lixiviation with a solution of sodium silicate (Na 2 SiO 3 ) or potassium phosphate (KH 2 PO 4 ). Sodium oleate also creates a hydrophobic layer, which protects the surface of the iron sulphide, preventing further contact with the environmental oxygen (14).…”

Section: Protection Methodologymentioning

confidence: 99%