Acid Purification and Recycling for Mining Operations
VSEP™ Nanofiltration for Spent Acid Leach Solutions
Acid leaching is a foundational unit operation in modern hydrometallurgy. Oxide ores containing valuable metals are routinely crushed, ground, and leached using mineral acids—most commonly sulfuric acid—to dissolve target metals such as copper, uranium, zinc, nickel, cobalt, and rare earth elements. Sulfide ores may be pre‑oxidized by roasting or pressure oxidation and subsequently leached using acid.
The resulting metal‑bearing liquor is known as pregnant leach solution (PLS). After metal recovery through solvent extraction, ion exchange, or precipitation, what remains is a spent leach solution—often still containing high acid strength but contaminated with residual metals, hardness, silica, and fines.
The Industry Challenge: Spent Acid Handling
Across mining, fertilizer, and specialty metals facilities, spent acid is typically:
- Neutralized and disposed, or
- Stored in lined ponds, creating long‑term environmental liabilities.
Both options carry significant cost, safety, and regulatory risk. Neutralization permanently destroys valuable acid and generates large volumes of sludge, while storage ponds create exposure to leakage, permitting challenges, and future closure liabilities.
Carbonate Ores: Compounding the Acid Problem
Carbonate‑bearing ores introduce a second layer of complexity during acid leaching. When sulfuric or hydrochloric acid contacts carbonate gangue, the acid is consumed irreversibly, forming metal sulfates or chlorides while releasing CO₂ gas.
This leads to several well‑known operational challenges:
- Excessive acid consumption
- Carbonate neutralization before complete metal recovery
- Situations where acid cost exceeds metal value
- CO₂ evolution disrupting heap permeability
- Gypsum formation fouling heaps, piping, and downstream equipment
Acid Leaching vs. Other Extraction Routes
Acid leaching is widely used for:
- Copper
- Uranium
- Zinc
- Nickel and cobalt (laterites)
- Rare earth elements
It is not typically used for metals such as antimony, aluminum, iron, chromium, molybdenum, or tin, which rely on alternative pyrometallurgical or alkaline processes.
For phosphorus and boron, acid leaching is the primary extraction method. In these applications, sulfuric acid digestion produces phosphoric acid or boric acid as the desired product—but purification is still required to remove magnesium, calcium, iron, organics, radionuclides, and other impurities before the acid can be sold or converted into downstream products.
VSEP™ Nanofiltration for Acid Purification and Recycling
Recover Acid. Remove Metals. Eliminate Disposal.
VSEP™ (Vibratory Shear Enhanced Process) nanofiltration provides a proven, industrial solution for purifying spent acid leach solutions and acid products—allowing acid to be recycled instead of neutralized and discarded.
New Logic Research has developed and deployed strong acid‑tolerant nanofiltration (NF) membranes capable of operating in up to 30% sulfuric, phosphoric, boric, or hydrochloric acid. These membranes selectively reject multivalent ions—including metals and hardness—while allowing monovalent acids to pass.
Why VSEP Is Different
Unlike conventional crossflow membrane systems, VSEP uses torsional oscillation of the membrane pack, generating extremely high shear at the membrane surface. This provides key advantages in acid service:
- Suppression of gypsum scaling
- Resistance to fouling by metals and silica
- Stable flux at high acid strength
- Minimal pretreatment requirements
- Effective cleaning using hot water rinses
This combination of acid‑tolerant membranes + vibratory shear makes VSEP uniquely suited for acid recycling applications that defeat conventional membrane systems.
Proven Performance: Pilot and Field Results
New Logic has conducted dozens of pilot studies on real mining and chemical acid streams. Typical results show high rejection of dissolved metals with minimal acid loss.
Representative rejection performance (selected examples):
| Graphite Mine | Al | Ca | Cu | Fe | Mg | Si | H2SO4 |
| 25% Sulfuric | 97% | 82% | 91% | 97% | 95% | 42% | 2% |
| Zirconium Mine | Ca | K | Fe | Mg | Na | Zr | H2SO4 |
| 18% Sulfuric | 76% | 0% | 90% | 87% | 37% | 96% | 1% |
| Rare Earth Mine | Al | Ca | Fe | La | Mg | Si | H2SO4 |
| 10% Sulfuric | 65% | 54% | 59% | 64% | 60% | 14% | 4% |
| Rare Earth Mine | Al | Ca | Fe | La | Mg | Si | P2O5 |
| 18% Phosphoric | 66% | 60% | 63% | 67% | 62% | 20% | 2% |
| Copper Mine | Co | Cu | Fe | Mg | Mn | Si | H2SO4 |
| 8% Sulfuric | 65% | 49% | 71% | 65% | 62% | 18% | 2% |
| Phosphate Mine | Ca | Cd | Cr | Fe | Mg | Zn | P2O5 |
| 26% Phosphoric | 83% | 82% | 96% | 96% | 86% | 78% | 2.5 |
| Precious Metals | Al | Ir | Ni | Pt | Rh | Zn | HCl |
| 25% Hydrochloric | 92%` | 88%` | 82%` | 44%` | 82%` | 51%` | 2% |
Rejection values shown are typical pilot results obtained using site‑specific solutions. Actual performance depends on acid strength, impurity profile, temperature, and recovery rate.
Acid‑Tolerant NF Membranes Designed for Longevity
Most commercial nanofiltration membranes—made from polyamide and polysulfone—are limited to a pH range of 3–10. Claims of “acid resistance” often mean shortened service life under aggressive conditions.
VSEP uses a true acid‑tolerant NF membrane chemistry, validated through:
- Long‑term soak testing in 25–30% sulfuric acid
- Multi‑year full‑scale installations
These membranes maintain rejection performance over time, avoiding the degradation seen with conventional “acid‑resistant” NF products.
The graph below shows the results of soak testing in 25% sulfuric acid and compare the magnesium sulfate rejection over time for the VSEP acid tolerant membrane and two other acid “resistant” NF membranes.
Case Study – East Coast United States
In 2017, New Logic installed a VSEP acid tolerant NF system for a phosphoric acid processing plant. The confidential client was previously calcining the acid to remove organics and volatile impurities. This process is very energy intensive and can also emit pollutants into the air. The system continuously processed 60 gpm of 30% phosphoric acid at a recovery rate of 70% under normal plant operations. The system achieved 70% reduction in TOC and about 90% reduction in magnesium, which is important when the acid is converted into fertilizer pellets.
Purified Phosphoric Acid with VSEP NF
Case Study – Fertilizer Plant in Spain
In 2007, New Logic installed a VSEP NF system to purify 18% low grade phosphoric acid to remove organics and impurities at a small facility in Spain. This purification was needed to improve the low grade acid to an acceptable level so it could be used as merchant grade acid that would be turned into phosphate fertilizer.
Case Study – Rare Earth Mine, Australia
New Logic has completed one year of test work for a rare earth mining project in central Australia for Arafura Rare Earths. New Logic has completed Front End Engineering Design (FEED)and is scheduled to install a large VSEP NF system to purify two acid streams that are generated in the process. The ore being mined is high in Phosphorus and when acid leaching is performed, a dirty phosphoric acid is produced. The VSEP system will be used to purify this acid and remove Uranium, Thorium, and other metals to meet merchant grade acid requirements. Also, another VSEP NF system will be used to purify a spent sulfuric acid leach solution so it can be recycled.
Key Benefits of VSEP Acid Purification
VSEP’s unique acid tolerant NF membrane combined with torsional vibration of the membrane provides an effective option for purifying spent acid leach solutions so the acid can be recycled instead of being neutralized and disposed of. VSEP can be used in the same way to purify phosphoric and boric acid to meet merchant grade quality for sale.
The VSEP system requires little pretreatment and can tolerate suspended solids loading due to wide spaces between the membrane sheets. The VSEP system is built using special alloys and materials of construction compatible with all kinds of acids. Shear generated from the oscillation of the membrane suppresses gypsum scaling and fouling allowing for steady flux rates and effective cleaning with hot water rinses. A VSEP NF system for acid purification has many advantages:
- Reduce fresh acid consumption
- Eliminate neutralization and disposal
- Lower overall operating costs
- Remove the need for spent acid ponds
- Recover residual metals from acid streams
- Improve product acid quality for sale or reuse
New Logic Research has designed, piloted, and commissioned VSEP™ nanofiltration systems in active mining, fertilizer, and chemical plants operating continuously under high‑acid, high‑fouling conditions. These systems have been operated for multi‑year periods in sulfuric, phosphoric, and hydrochloric acid service, providing direct operating feedback used to refine membrane chemistry, mechanical design, and cleaning protocols.
Pilot Testing: De‑Risk Your Project
Every ore body and leach solution is unique. VSEP nanofiltration does not replace every purification method—but it complements and enhances conventional processes by breaking equilibrium limits and enabling closed‑loop acid management.
New Logic provides pilot‑scale testing to confirm:
- Metal rejection
- Acid recovery
- Flux stability
- Cleaning effectiveness
VSEP nanofiltration is most effective when acid recovery and impurity removal are limiting factors. In cases where acid concentrations are very low, solids loading is excessive without screening, or acid reuse is not permitted by process constraints, alternative treatment strategies may be more appropriate. Pilot testing is used to confirm technical and economic suitability before full‑scale deployment.
This page was authored and technically reviewed by senior process engineers at New Logic Research, Inc., with over 30 years of combined experience designing, piloting, and operating industrial membrane systems for mining, precious metal refining, fertilizer production, and high‑solids wastewater treatment.
Get Started
If you are evaluating ways to reduce acid consumption, recycle spent leach solutions, improve product acid quality, or eliminate wastewater risk, VSEP can help.
- Request a performance projection: info@vsep.com
- Learn about the technology: https://www.vsep.com/technology/
- View Phosphoric Acid Clarification: MF VSEP Clarification of WPA
- View Phosphoric Acid Purification Case Study: NF Purification of Phosphoric Acid
About New Logic Research and VSEP™
- Over 450 VSEP systems installed worldwide
- Protected by U.S. and international patents
- Applied in mining, chemicals, power generation, and wastewater
- Engineering team with deep experience in hydrometallurgy, refining, membranes, and solids handling
Frequently Asked Questions (FAQ)
What is spent acid leach solution in mining?
Spent acid leach solution is the liquid remaining after valuable metals have been removed from a pregnant leach solution (PLS). While much of the dissolved metal has been recovered, the solution often still contains high acid strength, residual metals, hardness (calcium, magnesium), silica, and fines. Traditionally, this spent acid is neutralized and disposed or stored in ponds, which destroys valuable acid and creates long‑term environmental liabilities.
Why is neutralizing spent acid a problem?
Neutralization permanently consumes sulfuric, phosphoric, or hydrochloric acid—one of the highest operating costs in many leaching circuits. It also generates large volumes of metal‑bearing sludge, increases reagent consumption, and requires disposal infrastructure. Storage ponds introduce permitting challenges, closure costs, and risk of leakage or environmental release.
Can spent acid be recycled instead of disposed?
Yes—if the acid can be purified. Nanofiltration (NF) allows dissolved metals and multivalent ions to be removed while allowing purified acid to pass through the membrane. This enables acid recycling back to the leach circuit, reducing fresh acid purchases and eliminating neutralization.
What makes VSEP nanofiltration different from conventional NF systems?
VSEP uses torsional vibration of the membrane pack, generating very high shear at the membrane surface. This suppresses fouling and scaling—especially gypsum (CaSO₄)—which rapidly disables conventional crossflow membrane systems when treating acid streams.
In addition, VSEP uses true acid‑tolerant NF membranes, not standard polyamide membranes with limited pH resistance.
Will VSEP nanofiltration foul or scale in carbonate systems?
Carbonate‑bearing ores are notorious for gypsum scaling and hardness fouling. VSEP’s high shear environment dramatically reduces scale formation and allows stable operation even in streams with high calcium, magnesium, and sulfate levels. When fouling does occur, membranes can often be cleaned with hot water rinses, minimizing chemical cleaning requirements.
Does VSEP remove metals from acid?
Yes. VSEP NF consistently removes 50–95%+ of dissolved metals, including aluminum, iron, calcium, magnesium, copper, zinc, cobalt, manganese, rare earth elements, uranium, and thorium—while allowing the majority of the acid to pass through for reuse.
Can VSEP be used for phosphoric acid purification?
Yes. VSEP nanofiltration has been successfully used to purify wet‑process phosphoric acid (WPA), removing magnesium, calcium, iron, cadmium, chromium, zinc, and organics. This improves acid quality for fertilizer production or merchant‑grade sale and can replace energy‑intensive calcination steps.
Can VSEP purify boric acid or hydrochloric acid?
Yes. VSEP NF has been applied to boric acid, hydrochloric acid, and mixed acid systems, removing metals and hardness while allowing acid recovery. The system materials of construction and membrane chemistry are compatible with a wide range of aggressive acid environments.
Is VSEP a replacement for SX‑EW, precipitation, or evaporation?
VSEP does not replace metal recovery technologies such as SX‑EW or precipitation. Instead, it complements them by addressing acid recovery, impurity removal, and recycle limitations that equilibrium‑based processes cannot overcome.