Variation of green liquor dregs from different pulp and paper mills for use in mine waste remediation

Utilization of pretreated green liquor dregs as an activator for blast furnace slag: Effect on hydration, phase assemblage, and rheology

This study explores the utilization of calcium- and magnesium-rich pulp mill residues, i.e., green liquor dregs (GLDs), as an activator for ground granulated blast furnace slag (BFS). The aim of this study is to examine the potential of this unutilized residue when used as a part of alkali-activated materials (AAMs) and in this way enhance the exploitation of GLD. This study focuses on the fresh- and hardened-state properties of the produced paste and mortar samples, where 70% of BFS and 30% of GLD have been incorporated. Two different-sourced and thermally pretreated (105 °C, 300 °C, and 525 °C) GLDs have been used. The effect of thermal treatment on the utilization possibility of GLDs with respect to viscosity, setting times, reactivity, mineralogy, and microstructure is analyzed using the paste samples, while its effect on workability, and strength gain is measured using the mortar samples. Results show that both GLDs enhance the hydration of BFS and that the early-age hydration and strength increase when the GLDs have undergone pretreatment at the highest temperature (525 °C). However, at the later age (28 days), the samples activated with the GLDs treated at 300 °C achieve the highest strength. The addition of both GLDs treated at any temperature increases the viscosity of the composite samples and reduces their workability; however, it should be noted that optimization of water to binder ratio was not the objective of this study. The results of this study show that GLD, previously considered unreactive, can potentially become a reactive component of AAMs.

Chemical characterization of green liquor dregs from 16 Swedish pulp and paper mills between 2017 and 2019

Green liquor dregs (GLD) is an alkaline by-product from the pulp and paper industry with a pH between 10 and 14. Today most of the produced GLD in Sweden is landfilled. As a fine-grained alkaline material, it might be possible to use it for acid-generating mining waste remediation. To increase the utilization, quality characteristics and environmental performance need to be determined. In this study samples were collected 5 times from 16 mills during a period of 2.5 years, and were characterized by analyzing dry matter content, loss on ignition (LOI) 550 °C and LOI 950 °C, elemental analysis, pH, electrical conductivity, and calorific value. The results were then evaluated using multivariate statistics (PCA) as well as being compared to other studies and Swedish till. The results show that even if GLD is heterogenous (both within a mill and between different mills) trends can be seen for samples from most mills. When samples do stand out, it is predominately related to the same four mills. Most of the studied parameters showed characteristics favorable for use as a remediant; however, TOC, sulfur, and some of the elements require further study. In general, this study concludes that GLD can be a viable option for the remediation of small orphaned sulfidic mining sites and thus worthy of further studies on the interaction between GLD and acidic mining waste.Overall, GLD can be a good alternative for cost-effective remediation of smaller orphaned mining sites. It is readily available in large quantities, has the qualities needed for remediation of many orphaned acidic mining sites, and can often be locally sourced near the mining site. The use of GLD for mining site remediation is likely also a more sustainable method compared to traditional remediation methods.

SARS-CoV-2 removal with a polyurethane foam composite

The pandemic of COVID-19 (SARS-CoV-2 disease) has been causing unprecedented health and economic impacts, alerting the world to the importance of basic sanitation and existing social inequalities. The risk of the spread and appearance of new diseases highlights the need for the removal of these pathogens through efficient techniques and materials. This study aimed to develop a polyurethane (PU) biofoam filled with dregs waste (leftover from the pulp and paper industry) for removal SARS-CoV-2 from the water. The biofoam was prepared by the free expansion method with the incorporation of 5wt% of dregs as a filler. For the removal assays, the all materials and its isolated phases were incubated for 24 h with an inactivated SARS-CoV-2 viral suspension. Then, the RNA was extracted and the viral load was quantified using the quantitative reverse transcription (RT-qPCR) technique. The biofoam (polyurethane/dregs) reached a great removal percentage of 91.55%, whereas the isolated dregs waste was 99.03%, commercial activated carbon was 99.64%, commercial activated carbon/polyurethane was 99.30%, and neat PU foam reached was 99.96% for this same property and without statistical difference. Those new materials endowed with low cost and high removal efficiency of SARS-CoV-2 as alternatives to conventional adsorbents.

Co-disposal of lignite fly ash and coal mine waste rock for neutralisation of AMD

Waste rocks (WRs) from a lignite-producing coalfield and fly ash (FA) produced from the same lignite have been investigated in this study with a primary objective to determine the potential for co-disposal of WRs and FA to reduce the environmental contamination. Mixing WRs with FA and covering WRs with FA have been investigated. Particle size effect caused ≤2 mm particles to produce low pH (~2) and metal-laden leachates, indicating higher sulphide minerals' reactivity compared to larger particles (≤10 mm, pH ~ 4). Co-disposal of FA as mixture showed an instantaneous effect, resulting in higher pH (~3-6) and better leachate quality. However, acidity produced by secondary mineralisation caused stabilisation of pH at around 4.5-5. In contrast, the pH of the leachates from the cover method gradually increased from strongly acidic (pH ~ 2) to mildly acidic (pH ~ 4-5) and circumneutral (pH ~ 7) along with a decrease in EC and elemental leaching. Gradually increasing pH can be attributed to the cover effect, which reduces the oxygen diffusion, thus sulphide oxidation. FA cover achieved the pH necessary for secondary mineralisation during the leaching experiment. The co-disposal of FA as cover and/or mixture possesses the potential for neutralisation and/or slowing down AMD and improving leachate quality.

Inorganic Waste Generated in Kraft Pulp Mills: The Transition from Landfill to Industrial Applications

Kraft pulp mills produce the main raw material for paper, while several waste products are generated in large quantities in the process. This review study addresses four of the main inorganic wastes formed by this industry, namely green liquor dregs (GLD), slaker grits (SG), lime mud (LM) and boiler fly ash (BFA), which are still mostly discarded in landfills. A brief overview of a typical industrial process was included to outline the waste generation points. The main chemical and physical properties are indicated for highlighting the most relevant characteristics to determine which applications may be considered in each case. An in-depth literature review allowed the identification of the main applications that have been tested mainly at the laboratory scale and some at an industrial scale. The applications are grouped into construction materials, geotechnical, environmental, agricultural and others. This assessment shows that the circular economy and the sustainable development goals of the UN are important issues for organizations in general, and the pulp mill in particular. In fact, this industry has managed to close the chemicals loops, recover energy and reduce water consumption in the process. However, the current situation of inorganic waste can still be improved if industrial applications are developed to avoid landfill.