# Inorganic Waste Generated in Kraft Pulp Mills:
## 3 Main Properties of the Inorganic Wastes
### Mineral phases  
To select the best utilization option in each case, it is meaningful to identify the mineral phases that compose each material. For that purpose, XRD could be a valuable technique, in particular, to identify the crystalline phases, as indicated in Table 3. Accordingly, it can be concluded that calcite (CaCO\({}_{3}\)) is present in all wastes, whereas in a much more expressive quantity in GLD, SG, and LM. Besides calcite, GLD also contains dolomite (CaMg(CO\({}_{3}\))\({}_{2}\)), cesanite (Ca\({}_{2}\)Na\({}_{3}\)(SO\({}_{4}\))\({}_{3}\)(OH)) and pirssonite (Na\({}_{2}\)Ca(CO\({}_{3}\))\({}_{2}\).2H\({}_{2}\)O). Some references indicate that pirssonite is the dominant mineral [21; 29] in GLD, while others [31] indicate calcite as the most relevant phase. Sodium might be present in pirssonite, cesanite, natrite (Na\({}_{2}\)CO\({}_{3}\)) as well as sodium sesquicarbonate (Na\({}_{3}\)H(CO\({}_{3}\))\({}_{2}\)). Sodium and sulfur content result from the green liquor composition (mainly composed of Na\({}_{2}\)CO\({}_{3}\) and Na\({}_{2}\)S). In addition, brucite (Mg(OH)\({}_{2}\)) is commonly found in GLD.  
Regarding SG, besides CaCO\({}_{3}\), it may contain dolomite (CaMg(CO\({}_{3}\))\({}_{2}\)), pirssonite (Na\({}_{2}\)Ca(CO\({}_{3}\))\({}_{2}\).2H\({}_{2}\)O), portlandite (Ca(OH)\({}_{2}\)), larnite (Ca\({}_{2}\) SiO\({}_{4}\)). The high concentration of calcium-bearing mineral phases in SG results from the slaking reaction of quick lime with green liquor (aqueous solution of sodium hydroxide, sodium sulfide, and sodium carbonate) in the slaker unit. Moreover, quartz (SiO\({}_{2}\)), wustite (FeO) and brucite (Mg(OH)\({}_{2}\)) are also detected. Mg concentration in the SG can be related to the use of magnesium sulfate in the delignification process in some mills [19].  
As aforementioned, LM is formed in the causticizing reaction, and thus the main phase (more than 90%) is calcite [30], while some minor or trace phases may contain Mg, Si, Al, Fe, Na, K, P, and S, but normally not detected through XRD. Besides calcite, which is clearly identified in X-ray diffraction spectra, in the literature some minerals containing Ca and Mg carbonates have been identified (Ca\({}_{(1-x)}\)Mg\({}_{x}\)CO\({}_{3}\)) [31].  
With respect to BFA, the major minerals are quartz (SiO\({}_{2}\)), calcium-bearing minerals such as calcite (CaCO\({}_{3}\)), dolomite (CaMg(CO\({}_{3}\))), anhydrite (CaSO\({}_{4}\)) and portlandite (Ca(OH)\({}_{2}\)). Moreover, alumina (Al\({}_{2}\)O\({}_{3}\)), iron oxide (Fe\({}_{2}\)O\({}_{3}\)), periclase (MgO) and sylvie (KCl) also constitutes the BFA in variable amounts. In fact, BFA from coniferous trees tends to contain a higher amount of Si and Ca when compared to hardwood trees and relatively low K and S content [32]. The high calcite and aluminosilicate contents seem suitable as a cement replacement material and as aggregates for road construction [32]. Attention should be paid to sulfate and chloride content, which can be harmful in concrete applications. In particular, sulfate may lead to ettringite salts, which can cause cracks in the final material. Chlorides can provoke, for example, corrosion in reinforced concrete. Regarding the nutrients content, BFA is poor in nitrogen due to its volatilization during combustion and loss as gaseous compounds. On the contrary, the amount of K and P can be interesting for agronomic applications.