Using SEGR to Unlock Refractory Gold...
- E&MJ - Engineering & Mining Journal
- 2 days ago
- 6 min read
E&MJ - Engineering & Mining Journal - August 2026 | Processing Solutions
Some of the world’s largest remaining gold inventories are not hidden in unexplored mountains. They are already known, drilled and, in some cases, sitting above ground in tailings and spent heaps. Much of that gold is trapped in minerals such as pyrite and arsenopyrite, beyond the practical reach of conventional leaching.
RZOLV Technologies recently completed a 230-page technical study evaluating Sequential Electrochemical Gold Recovery (SEGR). The proposed low-pH, non-cyanide platform combines oxidative conditioning, optional copper removal, RZOLV gold complexation, activated-carbon recovery and solution recycle. The potential resource base is substantial, but the concept must still advance from promising chemistry to independently validated, heap-relevant metallurgy.
The Problem Is Access
The central scientific proposition behind RZOLV/SEGR is simple: refractory gold is often an access problem before it is a leaching problem. A gold particle may be soluble in cyanide, thiosulfate, thiourea, thiocyanate or another complexing system, but no reagent can dissolve gold if it cannot reach the metal surface.
In refractory ores, microscopic and submicroscopic gold may be enclosed within pyrite, arsenopyrite, chalcopyrite or other sulfide minerals. Those sulfides can also consume oxygen and reagents, form passivating compounds or interfere with downstream capture of dissolved gold.
The industry addresses this problem with pressure oxidation, bio-oxidation and roasting. Each method alters or destroys the sulfide host before gold leaching. Published studies illustrate the premise. In one bio-oxidation study, the proportion of monomer, or exposed, gold increased from 21% to more than 86%, followed by maximum thiosulfate leaching efficiency of 85.05%. In a separate high-pressure oxidation and jarosite-decomposition study, exposed gold reportedly increased from 4.23% to 80.4%, followed by gold leaching of 90.2%.
These results do not prove that RZOLV/SEGR will succeed. They support its central premise: changing the sulfide host can make previously inaccessible gold available for subsequent leaching.
The Low-pH Sequence
The RZOLV/SEGR study proposes a staged architecture built around low-pH oxidative conditioning, non-cyanide RZOLV complexation, activated-carbon recovery and closed-loop solution management. The distinguishing idea is not merely substituting one gold reagent for another. It is avoiding unnecessary reversal of the chemistry created during pretreatment.
Instead of oxidizing sulfides in an acidic environment, neutralizing the material and then returning to alkaline cyanidation, SEGR proposes to keep its principal stages within a broadly compatible low-pH range.
First, a low-pH oxidizing solution, potentially conditioned using oxidants generated electrochemically in a boron-doped diamond (BDD) cell, would contact and alter the sulfide matrix. The objective is to create porosity and microfractures, expose gold-bearing surfaces and maintain a controlled ferric/ferrous redox cycle.
Second, copper and other interfering base metals could be removed where the mineralogy supports it. This could create a by-product while reducing ligand consumption, oxidant demand, carbon co-loading and contamination of the recycled solution.
Third, RZOLV would be introduced only after pretreatment reached measurable mineralogical and chemical endpoints. Its proprietary sulfur-based ligand system would complex newly exposed gold within controlled pH and oxidation-reduction-potential (ORP) limits. Excessive oxidizing power is as undesirable as insufficient oxidation: too little leaves gold inaccessible, while too much may degrade the ligand, mobilize unnecessary impurities or promote passivation.
Finally, dissolved gold would be adsorbed on activated carbon, followed by elution, electrowinning and refining, as applicable. The barren solution would be reconditioned and recycled rather than routinely discharged.
This sequencing matters. Adding RZOLV directly to unoxidized refractory ore could consume valuable reagent on sulfides, copper, iron and other side reactions. The ore must first be transformed from a chemically complex refractory feed into conditioned material containing solution-accessible gold. SEGR is therefore a staged redox-management platform, not a reagent capable of dissolving gold that remains sealed inside intact sulfide grains.
The Mining Application Is Not Yet Proven
Individual elements of this architecture have scientific or industrial precedent. The Albion Process, for example, combines ultrafine grinding with atmospheric oxidative leaching of sulfide concentrates. Its commercial refractory-gold flowsheets generally oxidize finely ground concentrate in agitated tanks near pH 5.5 before conventional cyanidation. Albion therefore supports the broader principles of oxygen-based sulfide oxidation, mass transfer and passivation control, but it is not a direct SEGR analogue. SEGR proposes coarser, heap-relevant material, electrochemically conditioned low-pH solutions and non-cyanide gold leaching.
BDD is likewise an established industrial electrode material, although not proven in the proposed heap application. Element Six, part of the De Beers Group, announced a next-generation Diamox™ advanced-oxidation cell in 2016 using free-standing BDD electrodes for difficult industrial wastewater. The system drew on more than 20 years of electrochemical-oxidation research and was designed to generate highly oxidizing conditions in a robust, modular reactor.
RZOLV also has evidence for its standalone leaching component. Independent SGS laboratory tests reported 98.7% gold recovery from an oxide gravity concentrate and 89.4% from a sulfide gravity concentrate after 96 hours. A separate 73.5-metric-ton oxide vat test reported 67.51% overall gold recovery and demonstrated carbon adsorption and doré production. These results support the ability of RZOLV chemistry to dissolve and recover accessible gold on selected materials. They do not demonstrate refractory-gold liberation, electrochemical pretreatment or the complete integrated SEGR sequence.
That complete sequence has not yet been demonstrated in a representative heap-scale operation. Performance will depend on permeability, solution distribution, conductivity, current density, mass transfer, temperature, electrode durability, mineral variability and the ability to deliver oxidizing chemistry through an ore bed uniformly and economically. This is the central commercial question.
The Case for RZOLV/SEGR
The economic argument is based on stacked value rather than a single recovery number. A single-pad architecture could reduce repeated material handling, avoid separate oxidation and cyanide pads, limit major pH conversion and simplify solution management compared with a multistage, high-pH configuration. Those potential savings remain to be demonstrated by representative engineering and metallurgical work.
Copper could provide another value channel. In suitable polymetallic feeds, removing acid-soluble copper before gold leaching might generate by-product revenue. It could also improve the gold circuit by reducing competition for the RZOLV ligand and protecting activated carbon and the recycle loop.
SEGR does not need to recover the world’s entire refractory-gold inventory to become commercially relevant. It must identify a sufficiently large subset of feeds where incremental gold, silver and copper value exceeds the combined costs and risks of oxidation, electricity, acid, RZOLV reagent, carbon recovery, water management, residue treatment and environmental compliance.
The most realistic early market may not be the deepest, most intensely locked invisible gold. It may be partially oxidized tailings, spent heaps with poor historical solution contact, copper-bearing gold residues, and ores in which gold occurs near fractures or sulfide grain boundaries. These materials may require enough oxidation to expose additional gold rather than the near-complete sulfide destruction associated with an autoclave.
Non-cyanide Does Not Mean No Risk
A central attraction of SEGR is the possibility of recovering precious metals without adding cyanide during gold leaching. Any replacement must compete not only with cyanide chemistry, but also with more than a century of operating experience and an established international management framework.
Low-pH processing is not automatically benign. Oxidizing pyrite and arsenopyrite can mobilize arsenic, iron, sulfate and other constituents. Acidic treatment may also dissolve copper, manganese, zinc, nickel, cobalt, lead, mercury or antimony, depending on the feed. These species must be recovered, stabilized, recycled or treated. Final residues must be washed and neutralized, while waters and solids must demonstrate acceptable toxicity, leachability and long-term geochemical stability. The RZOLV/SEGR study therefore rejects descriptions such as “non-toxic,” “benign” or “discharge-free.”
For retreatment projects, recovering gold is not enough. A process that creates revenue while leaving the residue more acidic, mobile or toxic has not solved the closure problem. The environmental case will depend on before-and-after evidence showing that metal mobility, toxicity, water quality and residue stability have improved, or at minimum have not deteriorated.
Validation Will Decide the Platform’s Future
The next step is an independently managed, stage-gated metallurgical program. The study proposes a partner-sponsored 24- to 36-month validation effort estimated at $3 million to $4.5 million. It would progress from bench tests on representative feed composites to heap-relevant columns and then to a field demonstration of approximately 5,000 to 10,000 metric tons.
That work must prove five connected propositions: pretreatment measurably increases solution-accessible gold; RZOLV dissolves that gold at acceptable reagent and energy cost; activated carbon or another medium captures the dissolved precious metals without unacceptable fouling or losses; the barren solution remains recyclable without runaway accumulation of iron, copper, sulfate, chloride, salinity or ligand-degradation products; and treated residues and process waters meet defined environmental and closure endpoints.
If those propositions are validated together, SEGR could become a differentiated option for selected refractory ores, tailings and spent heaps. Until then, it should be presented for what it is: a technically grounded, testable processing hypothesis with meaningful upside and a clearly defined path to proof.
Duane Nelson is president and CEO of RZOLV Technologies Inc.
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