Concept

What Are Hydrotalcites?

  • Mg-Al sub-class of layered double hydroxides/hydrotalcites/anionic clays which are both naturally occurring and synthetically produced minerals.
  • Hydrotalcite structure is in the form of positively-charged mixed metal hydroxide layers separated by interlayers that contain water + exchangeable anions.


Fig-1

What Does Hydrotalcite Technology Do?

  • The technology uses commercially available additives to create synthetic hydrotalcite-minerals which can remediate and neutralise acidic wastewater and capture heavy metals such as uranium, copper, lead, cadmium and anions such as sulphate, chromate and arsenate.
  • As hydrotalcites form, metals and anions become trapped and are easily removed from wastewater streams within the hydrotalcite product.
  • The technology utilises abundant Fe, Mg and Al which are present in most acid mine wastewaters to create hydrotalcites, alternatively component reagents can be sourced and added. 
  • Optimal chemistry can be tailored to synthesise hydrotalcite formation – generally achieved by adding Mg and/or Al and then NaOH as a neutralising agent to remediate acidity.
  • The synthesised hydrotalcites can be captured and calcined to produce a stable spinel product or silicified to produce synthetic chlorite analogue for permanent storage or reprocessed to extract valuable high-grade metal by-products such as uranium and rare earth metals.

Where Can Hydrotalcite Technology Be Used?

  • Applications in mining, minerals processing and building industries, with particular relevance to regions where acidic wastewater requires neutralisation to avoid negative impacts on aquifers and soils.
  • Emerging global market as increasingly strict environmental management legislation impacts:
    • Existing/abandoned mine sites with acidic drainage/leakage, including mining waste heaps with oxidising sulphide minerals (such as pyrite);

    • in-situ uranium leach mine sites (“ISL”), for example leakage from thousands of cold war-era uranium injection/extraction bores in Europe and the US;
    • current mine closure policies are becoming increasingly rigid with requirement for long-term solutions for leakage of toxic by-products.
  • In areas of high environmental sensitivity where reverse osmosis (“RO”) is required to produce discharge quality water, VCL can pre-condition RO feed by inexpensively and rapidly removing foulants to achieve significantly enhanced efficiencies and cost reductions with reduced plant capacity requirements.

ISL Schematic

ISL Schematic

ISL Remediation Using “Virtual Curtain” Barrier

ISL Remediation Using “Virtual Curtain” Barrier