# Inorganic Waste Generated in Kraft Pulp Mills:
## 4 Potential Applications
### Boiler Fly Ash
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Application** & **Highlights** & **Scale** \\ \hline Construction materials & & \\ \hline
**Geopolymer concrete** & Replacement up to 10\% of the cement in concrete is feasible without virtually affecting the mechanical properties [23]. BFA has been successfully used with a silicon and aluminum oxides constitution of 80 wt \%, and the Si-to-Al ratio of 2 [76]. & Laboratory/ Industrial \\
**Geopolymer mortars** & BFA was used as the main source of aluminosilicate in the binder precursor (70 wt \% substitution to metakadin), comprising a binder-aggregate ratio of 1 to 5. All tested formulations belong at least to class M10 (UCS \(\geq\)10 MPa) [5]. BFA up to 75 wt \% were used as aluminosilicate source [29]. & Industrial \\
**Roller-compacted concrete** & Mixtures containing 10–20\% BFA + 50\% BBA (boiler bottom ash) & Industrial \\
**Rammed-earth construction** & BFA activated with a sodium-based solution was used to enhance residual granite soils properties for earth wall molds construction [78]. & Laboratory \\
**Clinker production** & Belitic and Portland clinkers were obtained. The chlorides present in the FA do not affect the durability of the clinker since most are eliminated during the thermal treatment [45]. & Laboratory \\
**Anorthite ceramics** & Formulations of 36 wt \% LM and 64 wt \% BFA produced anorthite with lightweight, high water absorption and good chemical stability [26]. & Laboratory \\
**Alkali-activated bricks** & Alkali-activated bricks can be produced using BFA with similar costs as the clay fired brick but with reduced environmental impact [79]. & Laboratory \\ \hline Geotechnical & & \\ \hline
**Filling mine cavities** & The fly ash originated from Stora Enso mills in Finland has been used as a hardener in filling mice cavities since 2003 [53]. & Industrial \\
**Stabilization of roads** & Improved road performance can be achieved by mixing existing unbound road bases with BFA without any other additives [80]. & Industrial \\
**Pavement construction** & A mixture of soil and wood FA (10 wt \%) showed to be a valuable material for hydraulically bound mixtures [81]. Alkali-activated low-calcium FA was successfully used as a binder for soil stabilization in road platforms [82]. & Laboratory \\ \hline Environmental & & \\ \hline
**Remediation of soils degraded by mining activities** & Granules of 90 wt \% BFA and 10 wt \% biological sludge improved soil quality (pH correction and extractable P and K), but were not able to support permanent plant cover [43]. & Laboratory \\
**Adsorbent** & Pb and Co removal from paint industries effluent reached 96.1\% and 99\% at pH 2 with a contact time of 3 h and 100 g/L wood ash [83]. BFA dosage of 160 g/L reduced COD by 37\% from real industrial wastewater [84]. & Laboratory \\ \hline Agricultural & & \\ \hline
**Liming material** & The soil extractable K and P increased, indicating that besides the limiting effect BFA can also contribute to improving soil fertility [25]. & Laboratory \\
**Soil amendment and fertilizer** & Ash levels up to 2 wt \% (40\) \%/ha), heat biomass increased more than with the control soil [40]. FA can be a potential soil fertilizer regarding some nutrient deficiencies [32; 38]. & Laboratory \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Applications of BFA reported in the literature. this waste as a self-hardening material for earth construction [87]. The use of BFA for the production of roller-compacted concrete applied in storage slabs is an application with large benefits that could be adopted inside the pulp and paper industry, reusing the wastes generated in the process in their own infrastructure (pavement of storage areas and roads in urban and forests locations) with economic and environmental benefits [77].