Adsorption of Cd (II) on Modified Granular Activated Carbons: Isotherm and Column Study

Role of grinding method on granular activated carbon characteristics

A coconut shell (AC1230CX) and a bituminous coal based (F400) granular activated carbon (GAC) were ground with mortar and pestle (MP), a blender, and a bench-scale ball milling unit (BMU). Blender was the most time-efficient for particle size reduction. Four size fractions ranging from 20 × 40 to 200 × 325 were characterized along with the bulk GACs. Compared to bulk GACs, F400 blender and BMU 20 × 40 fractions decreased in specific surface area (SSA, -23% and -31%, respectively) while smaller variations (-14% to 5%) occurred randomly for AC1230CX ground fractions. For F400, the blender and BMU size fraction dependencies were attributed to the combination of (i) radial trends in the F400 particle properties and (ii) importance of shear (outer layer removal) versus shock (particle fracturing) size reduction mechanisms. Compared to bulk GACs, surface oxygen content (At%-O1s) increased up to 34% for the F400 blender and BMU 20 × 40 fractions, whereas all AC1230CX ground fractions, except for the blender 100 × 200 and BMU 60 × 100 and 100 × 200 fractions, showed 25-29% consistent increases. The At%-O1s gain was attributed to (i) radial trends in F400 properties and (ii) oxidization during grinding, both of which supported the shear mechanism of mechanical grinding. Relatively small to insignificant changes in point of zero charge (pHPZC) and crystalline structure showed similar trends with the changes in SSA and At%-O1s. The study findings provide guidance for informed selection of grinding methods based on GAC type and target particle sizes to improve the representativeness of adsorption studies conducted with ground GAC, such as rapid small-scale column tests. When GACs have radial trends in their properties and when the target size fraction only includes larger particle sizes, manual grinding is recommended.

Organic soil additives for the remediation of cadmium contaminated soils and their impact on the soil-plant system: A review

Immobilization is among the most-suitable strategies to remediate cadmium (Cd) contaminated sites. Organic additives (OAs) have emerged as highly efficient and environment-friendly immobilizers to eradicate Cd contamination in a wide range of environments. This review article is intended to critically illustrate the role of different OAs in Cd immobilization and to highlight the key findings in this context. Owing to the unique structural features (high surface area, cation exchange capacity (CEC), presence of many functional groups), OAs have shown strong capability to remediate Cd polluted soils by adsorption, electrostatic interaction, complexation and precipitation. Research data is compiled about the efficiency of different OAs (bio-waste, biochar, activated carbon, composts, manure, and plant residues) applied alone or in combination with other amendments in stabilization and renovation of contaminated sites. In addition to their role in remediation, OAs are widely advocated for being classical sources of essential plant nutrients and as agents to improve the soil health and quality which has also been focused in this review. OAs may contain considerable amounts of metals and therefore it becomes essential to assess their final contribution. Elimination of Cd contamination is essential to attenuate the contaminant effect and to produce the safe food. Therefore, deployment of environment-friendly remediation strategies (alone or in combination with other suitable technologies) should be adopted especially at early stages of contamination.