pH Zero : the vision

Law of Conservation of Mass: “Nothing is created, nothing is destroyed, everything is transformed”.
Antoine Laurent de Lavoisier (1743-1794)

The deoxidation reactions of natural stone obviously do not escape this fundamental principle of che-mical physics.

The presence of iron in stone materials is common in nature; when in contact with water molecules it easily becomes rust (in chemistry, Ferric Oxide Fe₂O₃), with chromatic variations ranging from brown to yellow.

The “mission” is to remove these chromatic variations from the material, as they are not accepted by the market.

Therefore (provided that these color variations are caused by rust), the process consists in transfor-ming Ferric Oxide Fe₂O₃, in all its polymorphic crystalline variants, into another chemical form that can be removed—thus restoring the natural color of the stone, free from oxide contamination.

The transformation of Ferric Oxide Fe₂O₃ is achieved through formulations including different types of acids— often strong acids with high chemical affinity or reactivity with silicon. The lithic morpho-logical characteristics of the material—such as micro-fractures, porosity, and absorption coefficient—determine the quantity of formulation required per m².

pH Zero: the philosophy behind the plants

PH ZERO is Prometec’s industrial solution for surface acidetching and deoxidation treatment.

PH ZERO allows the automation and optimization of physical parameters in the treatment of stone materials, following the protocols recommended by chemical formulation suppliers.

Mastering these parameters means making the deoxidation process more efficient and faster.

The key parameters to be controlled are: temperature, time, ventilation speed, and quantity of formula-tion per m².

With PH ZERO, Prometec—drawing on its extensive experience in treatment lines—offers a customizable, ondemand solution to automate the protocols required for different formulations and production needs.

The materials and components of PH ZERO lines are carefully selected and engineered to work with highly aggressive acidic formulations (pH 0).

pH Zero: the description

Work cycle type

PH ZERO generally operates in batch mode, so the project is designed around the number of slabs to be treated daily, following the supplier’s protocol (times, temperatures, dosages, etc.). Where protocols allow, it can also work continuously, like a standard resin line.

Loading

At loading, as in resin lines, the slab is placed directly on the trolley. Depending on the fragility of the material and the need for book-match (if it is the first processing stage), a wide range of loa-ding/unloading robots—already in use in resin lines—can be chosen. Especially with translucent materials, it is possible to process slabs in double face mode: after treat-ment of one side, a second cycle (identical or different) can be applied to the opposite side by automa-tically reintroducing the slab into the plant.

Preparation

To enhance the action of the acid formulation, slabs can undergo preliminary preparation, such as drying and thermal treatment (even at low temperatures) to inhibit the evaporation of volatile compo-nents in the formulations.

Acid formulation application

The system automatically measures the surface and applies the quantity of formulation per m² recom-mended by the supplier.

The recommended dosage depends on the lithic matrix of the material—such as quartz or quartzites—with its apparent porosity and absorption coefficient. True “recipes” can thus be set for each type of material.

This ensures stoichiometric balance in the deoxidation reactions, thus optimizing the process.
The recommended dosage depends on the lithic matrix of the material—such as quartz or quartzites—with its apparent porosity and absorption coefficient. True “recipes” can thus be set for each type of material. This ensures stoichiometric balance in the deoxidation reactions, thus optimizing the process.

Recommended quantities: generally 50–100 g/m².
Application takes place inside a controlled-atmosphere cabin.

Reaction or “curing”

After application, the slab is transferred via elevator to a silo-reactor for curing.
Temperature is controlled; heating is provided by a resistance battery; ventilation is laminar-flow across slabs, with programmable speed. Curing is performed at desired temperature and ventilation speeds, enabling concatenated cycles with temperature–ventilation combinations. A second application of formulation, reactive, or solvent can be concatenated: the slab is removed from the silo-reactor, treated again by spill-roll, and reintroduced into the silo-reactor with the required time, temperature, and ventilation. During residence in the silo-reactor, optional post-curing can evaporate excess components by auto-matically adjusting temperature and ventilation speed.

At the end of the cycle, for removal of solid reaction products, slabs can undergo online washing with brushing and subsequent drying before unloading.