Landfill Mining and Reclamation

Basics

• Essentially Strip Mining but of Landfills
• Easier with modern landfills, but can be done with old (even informal) ones.
• In older ones, it can even be of historic value (like a time capsule of sorts, anthropologists, and archeologits do this with old "mounds" with mainly shells and bones of food, but this is a similar modern form)
• Leads to:
  • Recovered Recyclable Materials (Metal, Glass, Plastic, Misc)
  • Recovered Soil/Clay (cover material)
  • Recovered Aggregate Materials
  • Sometimes Methane Gas (if captured and not released)
  • Typically large Sulfur Compound Gasses, and Mixed Chemical Leachate, which is toxic, but can be processed into useful products
  • Refuse Derived Fuel (sort of like biomass, but much more unpredictable)
    • This can in turn be made into Syngas and Slag
• Finally the land is returned to it's natural state and/or develped

Challenges

• Nastiness of the work site
  • Although Dedicated “Work Clothes” / “Junk Clothes” + Boots and a “Wash Out” + swap clothes and boots based Contamination Reduction Zone can help with this
  • Also Automation/Mechanization or things like PAPR Helmets with Granulated Activated Carbon cartridges
• Unknown/Varying Composition of the Landfill
  • Modern landfills are a sort of cursed Lasagna of MSW , Landfill Daily Cover , and small amounts of Construction and Demolition Debris
  • Compared to a more homogeneous Ore Vein / Petroleum Resevoir this can lead to challenges
  • Also unknown hazmat that sneaked in such as in Disposable Vape Pens or Cell Phones etc
• Hazards
  • Combustible/Explosive Atmospheres (from accumulated Landfill Gas )
  • Subsidence of the landfill as contents and/or daily cover are biodegraded
    • While Compactor Tires tend to be used, gradual compaction of the overall landfill may contribute to this as well

Stages

Background

• First you have the original stages of a landfill’s lifespan
• The part where landfill mining would take place would largely be in if it is NEAR capacity (and they are trying to “squeeze some extra capacity out” so to speak), or in a completed/OLD landfill that is being mined due to liner failure, economically recoverable materials, or as a broader government policy of Landfill Phase Out
• The main thing to consider is how stabilized is the landfill overall, is there still non-capped/covered sections one would be driving on, and how that impacts things.

Stabilization

• There may be an advantage to let things ferment/stabilize for a bit, akin to a Wet Material Recovery Facility albeit Landfill Gas and Landfill Leachate are far “dirtier” products to do with
  • Also recoverable non-biodegradable materials will potentially degrade in this period reducing value
    • Metals rusting, plastics being degraded (Think a BRAND NEW plastic bottle vs Litter on the side of the road that is heavily weathered)
    • Things such as electronics and batteries may become especially degraded/harder to separate out (although CITATION NEEDED)
• One thing to note is if a Landfill got to the “stabilized” level where Landfill Gas is no longer being created, the Landfill as a whole could be Inerted
  • This would HEAVILY reduce, if not eliminate Fire/Explosion Risk (at least in the context of Landfill Gas, Hazmat+Reactive Metals etc may still start smaller fires)

Pre-Treatment

• This may occur along with, or after Stabilization

Steam

• One Commercial Off The Shelf option is Steam Injection
  • Parts Commonality with Enhanced Oil Recovery
  • POTENTIALLY a Just Transition in terms of climate change adaptation, although again quality of life concerns are CRITICAL to that
• Supposedly aids LFG production, also may help melt and consolidate plastics/do something akin to In-Situ Thermal Remediation where contaminants may be essentially Steam Distilled / “Sparged” Out

(Auto-) Thermal

• Landfill Fires already happen by accident
• Although especially as they near completion (of a cell) they can be controlled by adjusting the air inlets/fans (akin to a Wood Stove Damper
• In a similar manner to Coal Seam Fire->Underground Coal Gasification, i postulate one could do In-Situ Landfill Gasification
  • If not high quality syngas generation, the Thermal Processing may be of use in of itself (more akin to Incineration , where waste reduction is the goal not the energy produced by it)

Perforation

• Due to Daily Cover, and how landfills are sometimes arranged as a stack of sealed “cells”, rather than one monolithic pile, Perforation of those Cells/Daily Fill upon Completion or Before Exploitation may aid in In-Situ Processes/Venting+Inerting the landfill
• This also may aid in leachate removal/drying

In-Situ Leaching

• Via technology similar to mining in terms of liquids used and downstream processing, the Leachate System may be adapted to an In-Situ Leaching system.
• Bio-Mining may carry less risk, while more conventional Acid Leaching may be more effective (although compatibility with Liner and Pipe material must be documented and considered)
• More novel solutions such as Ionic Liquids or things like Iron(III) chloride ( Ferric Chloride ) may work

Leachate Removal and Drying

• In modern landfills ( Bioreactor Landfill ) leachate is recirculated from the bottom of the landfill to the top to aid the biodegradation
• Before final excavation (regardless of prior pre-treatment processes/in-situ recovery methods) this will need to be minimized if not removed altogether
  • Methods to reduce leachate remaining / the benefits of concentrating it vs additional costs flr disposal of said concentrated leachate etc are worth analyzing
• Removal of Piping/Monitor Wells may aid in later excavation/drilling as well
• Alternatively adding in more pipes for air/suction, or even removing the top “Cap” section of the liner/clay to allow for faster drying may be beneficial
  • Potentially replacing the impervious top cap with a layer of Biochar or similar material such as Granulated Activated Carbon would allow for it to “breathe” while also providing Odor Emissions Controls

Excavation/Earthworks

• While MOSTLY similar to any form of Excavation / Open Cut Mining etc, there are some special aspects to be aware of
  • Aforementioned Hazards unique to Landfill Mining
  • Potential (Modern) Archeological Value / Criminal Evidence (Buried Remains etc)
• Otherwise it would probably be Dozers and Excavators / Front End Loaders etc loading debris into Dump Trucks or [Roll Off Boxes]] or some similar container to be moved to the New Landfill, Materials Recovery Facility or W2E plant etc
• Another thing to consider is if special Tires/Tracks would be needed
  • Also either planned time, or specially designed mechanisms to remove tangled trash and other debris from axles and other spinning points

Final Site Renovation/Remediation

• Finally any temporary gear would be moved out and either a new liner be placed and “rinse and repeat”, or all remnants of Landfill Infrastructure would be removed and the sight either Rewilded (akin to Mine Reclamation ) or Leveled and developed for higher level uses (Such as Farmland, Housing, Mixed Use Development etc)

Known “Reserves”

Backround

• In conventional mining and fossil fuels, there is the concept of known reserves (Known Formations that Can Be Exploited”
  • Subcategory of “Proven/Working Reserves” of Formations that are being exploited, but have a certain capacity still left
• Related (as per Unconventional Oil etc) is how what CAN be done (technology wise) drives what you consider usable
  • This is less relevant to Landfill Mining, although locating Unofficial Illegal Dumping sites/accumulation of Marine Litter in certain “choke points” etc may have a similar effect of constantly moving the “peak”
  • Another category would be reprocessing of Hazmat/Nuclear Waste etc (Going from “noone would ever use that” to “converting asbestos to allotropes without asbestos fiber type issues” (solid slag etc))

To-Do

• Number of:
  • Conventional (ie MSW not HazMat Landfills , Coal Bottom Ash Damns , etc) Landfills in the relevant regions
    • To reduce Scope Creep , a single country such as the USA, or even single state approach may be more reasonable
  • MRF Plants
  • W2E Plants
  • More details on Composition of MSW
    • Although this probably varied with location and era the waste was deposited

Internal Links

• Gasification
• Recycling

External Links

• The Wikipedia Page on Landfill Mining and Reclamation