Retention of Cd, Cu, Pb and Zn by Wood Ash, Lime and Fume Dust

Abstract

Heavy metals are of interest due to their deleterious impacts on both human and ecosystem health. This study investigated the effectiveness of wood ash in immobilizing the heavy metals Pb, Cd, Cu and Zn from aqueous solutions. The effects of initial metal concentrations, solution pH, ash dose and reaction time on metal sorption, as well as the metal sorption mechanisms were studied. To investigate the effect of initial metal concentrations, solutions containing Cd, Zn (25, 50, 75, 100 or 125 mg L −1 ), Cu (25, 50, 75, 100, 125, 150 or 175 mg L −1 ) or Pb (250, 500, 750, 1000, 1250, or 1500 mg L −1 ) were reacted with 10 g L −1 ash for two hours. For the effect of pH, solutions containing 100 mg L −1 of Cd, Cu or Zn or 1500 mg L −1 of Pb were reacted with 15 g L −1 ash over a pH range of 4 to 7. The wood ash was effective in immobilizing the four metals with a sorption range of 41-100 %. The amounts of metals retained by the ash followed the order of Pb > Cu > Cd > Zn. As expected, absolute metal retention increased with increasing initial metal concentrations, solution pH and ash dose. Metal retention by the ash exhibited a two-phase step: an initial rapid uptake of the metal followed by a period of relatively slow removal of metal from solution. Metal retention by the ash could be described by the Langmuir and Freundlich isotherms, with the latter providing a better fit for the data. Dissolution of calcite /gypsum minerals and precipitation of metal carbonate/sulfate like minerals were probably responsible for metal immobilization by the ash in addition to adsorption.

Repeatable use of wood ash to remove lead from contaminated water

“…Therefore, our results indicate that the lead removal capacity of wood ash in this study was significantly superior to that reported by Chirenje et al [18] (101 mg g -1 ). As previously stated, the lead removal by wood ash attributed to hydrocerussite precipitation suggests that the high calcite content in the wood ash enhanced the removal of lead.…”

“…As previously stated, the lead removal by wood ash attributed to hydrocerussite precipitation suggests that the high calcite content in the wood ash enhanced the removal of lead. The loss on ignition and calcium content of wood ash in Chirenje et al [18] were 250 and 42 mg g -1 , respectively; therefore, the organic matter content was higher and the calcite content was lower than those in the present study. Hence, the higher level of lead removal observed in this study is attributed to the low organic matter and the high calcite content.…”

“…Therefore, these results indicate that the main mechanism of lead removal by wood ash is the precipitation of hydrocerussite. Chirenje et al [18] suggested that lead was removed by wood ash via the precipitation of a calcite-like mineral by ion exchange, whereas the present study shows that the reaction between lead ions and calcite in the wood ash induced the hydrocerussite precipitation. The kinetics sorption data show that the pH value of wood ash was stable for 1 h and then greatly increased (Fig.…”

“…However, previous reports on heavy metals removal by wood ash are very limited [17,18]. Chirenje et al [18] observed that the capacity of lead removal by wood ash was 101 mg g -1 and that wood ash could remove lead in solution by precipitating lead carbonate minerals. They also reported that wood ash could stably remove lead in a weakly acidic to neutral pH solution (pH 4-7).…”

Removal of Organic Pollutants from Wastewater Using Wood Fly Ash as a Low‐Cost Sorbent

“…Since the physicochemical properties of wood ash are similar to commercial AC, it is possible to use wood ash as an alternative low cost carbon sorbent for wastewater pollution treatment. Wood ash can remove metals [14,15] as well as organic compounds from the aqueous solution. Color, COD, and lignin from pulp and paper wastewater were precipitated with calcium contained in wood ash and were adsorbed on the surface of wood ash particles [16].…”