Physico-chemical treatment

Physicochemical units: treating inorganic waste

The physicochemical units at the Antwerp plant treat industrial liquid and solid inorganic waste. These units neutralise acids and bases, oxidise cyanides, reduce chromates and immobilise heavy metals. 
In specific cases, emulsion breaking (of oil-water or latex emulsions), precipitation (of dissolved metals) and dewatering of sludge by filter presses are also possible. One or more treatments can be used for very specific waste flows. 

We want to re-use as much residue as possible in our processes. In the physicochemical installations we replace auxiliary substances, such as lime and cement, with residues from our processes wherever possible. This way we save on raw materials.

IndaChem Liquids: treating liquid inorganic waste


Indaver accepts many different acids and bases. Quite often these are loaded with heavy metals and/or limited concentrations of organic components. This necessitates a combined treatment.

Waste flows that must be neutralised originate from cleaning activities (e.g. pickling, passivating and cleaning tanks), surface treatment of metals, etc.


Immobilisation is a technique to separate heavy metals, anions or salts from wastewater. Examples of wastewater are: water from scrubbers, liquid catalysts, various flush waters, etc.

Neutralised acids or bases loaded with heavy metals are treated in a second phase in this unit. Metals such as Cu, Zn, Ni, Co, Cd, Mn and Cr3+ are removed in a single process, while other metals, such as Hg, Tl, Pb and As, need treatment in several steps.

The anions that can be removed are sulphates, phosphates, fluorides and sulphides. No limitations in quantity or shipment format apply to this treatment.


Indaver can guarantee the oxidation of cyanide-containing waste and the oxidation of nitrite in limited concentrations.


Indaver can guarantee the reduction of hexavalent chrome up to Cr3. By adding active carbon, removable organic components can effectively be separated from the waste. The concentration of this is to a maximum of 1%. ‘Removable’ is understood to mean non-volatile, non-polar hydrocarbons, such as chlorinated solvents, aromatics, etc.

There are no absolute criteria for emulsion breaking and filter pressing of waste. A laboratory analysis will indicate the possibilities for emulsion breaking. Indaver usually works with a test load for filter pressing.


Physicochemical treatment creates sludge and wastewater. The sludge is dewatered in filter presses and subsequently transported to the landfill. The wastewater goes to the water purification plant for further treatment. The end-product – the filter cakes – of the immobilisation unit is not harmful and is transported to the Category 1 landfill according to the acceptance conditions as stipulated in VLAREM 2.

Sustainable approach to materials

In our processes, we want to replace as many precious primary raw materials as possible with waste. In IndaChem Liquids, we replace at least 50% of the slaked lime (almost 1,000 tonnes), which neutralises the contamination, with residues from our incineration process. In addition, we use acid wastes instead of iron (III) chloride (FeCl3), which saves another approx. 600m³ of raw materials.

Indachem Solids: solidification of solid inorganic waste

This physicochemical plant ‘solidifies’ waste products such as fly ashes, slags, filter cakes, catalyst waste, sludge, contaminated soil, boiler ash, residues of flue gas cleaning and certain types of salt waste. These waste products are immobilised with the aim of preventing impurities from behind released into the environment. The hazardous substances in waste are immobilised via a chemical or physicochemical procedure. The immobilised end-product is transported to our own landfill area (on the same site).

Indaver uses solidification processes to produce end-products that correspond as accurately as possible with natural solid materials. 


We unload the waste substances in silos where we add reagents, binding agents and fillers following a recipe developed by the laboratory. The mix neutralises and solidifies the waste substances. Then we mix it together, which results in a sand-like material. Heavy metals and/or anions are thus ‘chemically’ anchored in this sand-like end product. We load the end product into lorries immediately and transport it to the landfill site. There the material hardens further into one mass.

A sustainable and caring approach to raw materials

In our processes, we want to re-use as many residues. At IndaChem Solids, we partially replace cement with certain residues.

Continuous improvement

Over the years, the plant has been improved a number of times. The water management has been fitted with a slib pump that pumps a mixture of water and acids into the mixer. A batch mixer means that waste substances and additives can be measured out according to the mixing process. In 2013, IndaChem Solids acquired a new Eirich reactor. The reactor is essential because it is the heart of the plant. Thanks to the “Eirich” we can handle more complex recipes and reduce treatment time. 

Closing the materials loop

To avoid contaminating the sewage system on the site, we use rainwater from the solidification zone as process water. The percolate water from landfill is therefore given a second life as process water in the mixing process: the materials loop is closed. This innovation is the result of 25 years of experience and research and of an intensive collaboration between the different departments at Indaver.