António Fiúza (FEUP - Cerena) · Open Pit Mine Waste Rock Waste Rock Stripping Ratio 7.2:1 114...

Resíduos mineiros: Contribuições para a Economia Circular

António Fiúza (FEUP - Cerena)

Open PitMine

Waste Rock

Waste RockStripping Ratio 7.2:1114 Mm3

Processing

Ore15,9 Mm3

Mean Grade: 66 kg/ton

Tailings

Metallic Copper

1.05 Mm3

14.5 Mm3

Total Extracted Material – 129.9 Mm3

Total Wastes – 128.m3 Mm3

Percentage of Wastes – 98.53%

The Project ERA- MIN/0007/2014 has the financial support of FCT/MCTES through national funds (PIDDAC)

Improve Resource Efficiency and Minimize Environmental Footprint - REMinE

Ore Mined

Million Tons

Share of ore that becomes waste,

not including overburden (%)

Iron 25503 60

Copper 11026 99

Gold 7235 99.99

Lead 1077 97.5

Aluminium 856 70

Source: Gardner & Sampat (1998)

Principle 1: Preserve and enhance natural capital… by

controlling finite stocks and balancing renewable resource flows.

Principle 2: Optimize resource yields… by circulating products,

components, and materials at the highest utility at all times in

both technical and biological cycles.

Principle 3: Foster system effectiveness…

by revealing and designing out

negative externalities

TYPES OF MINE WASTES

1. OVERBURDEN2. WASTE ROCK3. LOW GRADE ORE4. TAILINGS5. HEAP LEACH SPENT ORES

What to do with the wastes?Conventional Solutions…

• Usage as construction material• Usage as backfill• Storage

New imaginative usages are required!

Next challenge will be the production with an almost null level of solid waste generation as it was possible in the recent

past to have mining facilities almost without industrial effluents.

SOLID PRODUCTS IN MINING

MAIN PRODUCT MAIN CONCENTRATE

SUB-PRODUCT OTHER MINOR CONCENTRATES

CO-PRODUCT Extracted Bedrock (Sand, Gravel,…)

OVERBURDEN Enveloping rock; normally easily

commercialized.

WASTE ROCK Huge quantities

RECYCLABLE TAILINGS Ex: Non sulfide and non-toxic

tailings

STORABLE, NON RECYCLABLE TAILINGS Ex: Pyritic tailings

NON-STORABLE, NON-RECYCLABLE

TAILINGS

Ex: Radioactives, High grades in As,

Hg,…

Largest dams ever built – seen from space

Unlike water dams, have to last “for ever”

Normally built progressively over a long period

– up to 50 years

Often built with non-engineering materials

Should be considered as a living entity

Żelazny Most (Poland)

1. Tailings with sulfides2. Radioactive tailings3. Tailings with high grades in toxic

elements (Ex: As)4. Tailings from Coal mines5. Highly Alkaline tailings

• Highly caustic nature of the red mud slurry • Extreme pH (13.1) and alkalinity (up to

6600 mg L−1 as Na2CO3), • Elements soluble at high pH, such as Al, As, Cr,

Mo, and V• Fine particle size, which once desiccated, can

generate fugitive dust

ALTERNATIVES

•Re-mining •Additive for cement industry•Civil construction – Roads, Pavements •Geo-cementation•Geo-polymerization

Example: Penouta Mine (Spain)Exploitable Reserves

Project of final shape tailings re-deposition

Mineral reserve model for the open pit re-extraction

Tailings re-extraction Project Final shape model of the pit

Different percentages of copper tailings as additive for cement were tried (2.5; 5 and 10%)

Copper tailings have a slight negative impact on the slump, setting time and porosity of mixtures. However, improved mechanical strengths and abrasion resistance, and reduced chloride penetration compared to the control specimens were observed in mixtures incorporating copper tailings.

Toxicity characteristic leaching test results revealed that the release of heavy metals from mixtures containing copper tailings is considerably lower than the Regulations.

The major goal is to develop an environmentally friendly and cost effective method for recycling and utilizing mine tailings as construction materials:

• Bricks• Concrete for pavement• Concrete for structures, e.g. bridges• Highway base material• Highway embankment material

Cement Hydration Reaction (Thomas, 2004):

xCaSiO + yH2O → xCaO.ySiO.zH2O + wCa(OH)2 + Heat Calcium Silicates + Water → Calcium Silicate Hydrate (C-S-H) + Lime + Heat

Geopolymerization consists of 2 basic steps:

(1) Dissolution of aluminosilicates by alkali to produce reactive silica and alumina.

(2) Polycondensation process leading to formation of amorphous to semicrystalline polymers

Advantages of geopolymer over PC

Abundant raw materials resourcesEnergy saving and environment protectionGood volume stabilityReasonable strength gain in short timeUltra-excellent durabilityHigh fire resistance and low thermal

conductivityAbility to immobilize toxic and hazardous

wastesSuperior resistance to chemical attack

New tailings deposition techniques such as PASTE OR CO-DEPOSITION allow for:

Simultaneous Remediation and production; Absence of environmental passives at the end

of life. Safe storage of wastes, and even toxic wastes,

from other industries in a more safe way than allowed by the landfills for toxic products.

FOR THOSE TAILINGS THAT CANNOT BE RECYCLED:

• In-Situ Immobilization• In-situ Solidification• In-situ Immobilization technologies using

various types of grouting, especially clays with iron micro or nanoparticles. Other types of nanoparticles.

• Geo-polymerization• Geochemical immobilization

In-situ immobilization

• Injection of grouting with Clays and nanoparticles in the tailings; this technology aims to inertize a solid contaminated source.

•The nanoparticles will oxidize and/or sorb the contaminant that will be incorporated into a solid matrix with very low permeability.

•The groundwater will be diverted and will not flow through the grouted contamination source.

In-situ immobilization

Possible options are: ① Physical encapsulation by creating solidified

monolith (In-situ grouting); ② Chemical inclusion in CSH and CAH by

isomorphic substitution and ③ Sorption on clay and pozzolanic reaction product

or cation/anion exchange④ Geochemical immobilization

ZVI Clay/Soil Mixing Process

ZVI Clay/Soil Mixing

In-situ geochemical stabilization –sequential injection of solutions that react in the aquifer to form a sparingly soluble solid with high adsorption capacity for the element of concern.

Cement Hydration Reaction (Thomas, 2004):

xCaSiO + yH2O → xCaO.ySiO.zH2O + wCa(OH)2 + Heat Calcium Silicates +Water → Calcium Silicate Hydrate (C-S-H) + Lime

–Reduces mobility of chemicals of concern

–Increases strength

–Reduces permeability

–Minimizes free liquid.

Geo-Solidification

Process forms a granular or monolithic solid that incorporates the

waste material

A solid matrix, calcium-silicate-hydrate (C-S-H) is formed in presence

of water

In-situ geochemical stabilization – sequential injection of solutions that react with the tailings forming insoluble compounds that include or sorb the toxic elements.

AND STILL

VITRIFICATION and IN-SITU VITRIFICATION…

① A new typology for mining wastes considering its recyclability potential is required. Specifications for each category must be defined.

② Recyclable tailings may be remined or used as additive for cement industry, utilized in civil construction, as for instance in roads, pavements or produce new elements of construction such as bricks by geo-cementation and geo-polymerization. Usage as backfill has also been a current practice during the last 60 years.

③ Storable, non recyclable tailings may be deposed in a safe way as paste. Tailings disposed as paste may be used commercially as a very safe confined system to store wastes from other industries. It is more safe than the landfills for toxic products currently used;

④ Non storable, non recyclable toxic tailings may be submitted to in-situ immobilization, in-situ solidification or immobilized by special grouting, with clays and nanoparticles; they also may be submitted to geo-polymerization or in-situ geochemical immobilization.

⑤ CIRCULAR ECONOMY IN MINING IS POSSIBLE (ENHANCING NATURAL CAPITAL, MAXIMIZING YIELD AND FOSTERING EFECTIVENESS)

⑥ FINALLY, many other applications are possible. USE YOUR IMMAGINATION .

António Fiúza (FEUP - Cerena) · Open Pit Mine Waste Rock Waste Rock Stripping Ratio 7.2:1 114...

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