Views: 140 Author: SEPPE Garnet Team Publish Time: 2026-09-24 Origin: SGA Blasting
Do you often confuse chloride content with conductivity?
Why do many manufacturers use conductivity testing to make a preliminary assessment of chloride levels?
Natural garnet is a group of silicate minerals; chloride ions (Cl⁻) are not a primary structural component of the garnet crystal itself. In this context, “chloride content” refers to Cl⁻ present in soluble salts found on the surface of garnet particles, within their pores, or as inclusions. What is measured is the mass fraction of water-soluble chloride ions (Cl⁻), typically expressed in ppm (parts per million) or mg/kg.
Controlling chloride levels is essential for ensuring application quality and equipment safety. Some chloride-containing salts are hygroscopic, while chloride ions can strongly promote electrochemical corrosion.
In abrasive blasting for anti-corrosion purposes, residual chlorides can cause flash rust and sub-film corrosion, leading to coating blistering, peeling, and delamination. Chloride ions trapped beneath the coating can continue to corrode the steel.
In waterjet cutting, the primary risks include abrasive clumping, abrasive feed line blockages, pitting corrosion on waterjet components, and subsequent rusting of the cut surface.
For alluvial and mineral sand garnets, raw materials may come into contact with saline groundwater, surface water, or seawater during deposition and mining. Chlorides can also be introduced during the washing process if high-salinity groundwater or recirculated water is used.
Beach garnet, having been exposed to seawater for extended periods, often accumulates crystallized salts, such as sodium chloride (NaCl) and magnesium chloride, on the particle surfaces. If subsequent sand-washing processes are inadequate, chloride levels can reach hundreds or even over a thousand ppm.
Laboratories can determine water-soluble chlorides in non-metallic blast-cleaning abrasives under ISO 11127-7:2022. ASTM D512-23 provides test methods for determining chloride ions in water and may be applied to a prepared aqueous extract where appropriate.
Sampling and Extraction: Weigh 100 g of garnet sand and add 100 mL of high-purity deionized water.
Agitation and Soaking: Vigorously agitate the mixture for 5 minutes, let it stand for 1 hour, and then agitate it again for 5 minutes to dissolve the surface salts.
Filtration: Filter the mixture to obtain a clear aqueous extract.
Chloride Analysis: Take a specified volume of the extract and determine the mass fraction of Cl⁻ using a chloride-specific analytical method, such as amperometric titration, spectrophotometry, or ion chromatography.
ISO 11126-10:2025 specification: Water-soluble chlorides ≤ 0.0025% (m/m) = 25 ppm.
SEPPE SGA alluvial natural river sand garnet: Water-soluble chloride 12–18 ppm (max 25 ppm).
Looking at these steps, you might notice that they resemble the procedure for measuring garnet conductivity.
The core sampling logic is similar: both methods can use an aqueous extract, but the analytical measurement is different.
Conductivity testing measures the total concentration of water-soluble conductive species. It does not identify the individual ions present or provide a quantitative chloride result. An exact chloride value therefore requires a chloride-specific analytical method.
Where the laboratory procedure has been validated for its intended purpose, the extraction sequence from ASTM D4940-25 can be used to prepare an aqueous extract for separate chloride analysis: mix 300 mL of garnet with 300 mL of water, stir for 1 minute, let it stand for 8 minutes, and stir again for 1 minute.
The extract must then be filtered and analyzed using a chloride-specific method, such as silver nitrate titration, spectrophotometry, or ion chromatography.
In garnet sand where chlorides account for more than 85% of the water-soluble salts, conductivity tends to increase with chloride concentration. Under a stable salt composition, conductivity testing can serve as a rapid and representative screening indicator of total water-soluble salts, including chlorides. However, it cannot replace a chloride-specific test when an exact chloride value is required.
To view the conductivity measurement procedure, watch the garnet abrasive conductivity test video and read the brief guide to garnet abrasive conductivity testing.
The guide explains the ASTM D4940 testing procedure and also covers ISO 11127-6:2022, including how the two methods are defined and where they differ.
