Optimising heavy metal adsorbance by dried seaweeds

Abstract

Industrialisation has resulted in large-scale production of anthropogenic pollutants, particularly heavy metals. Existing industrial techniques for the purification of waste water are expensive. A cheaper alternative may be 'bioremoval', that is, the accumulation and concentration of pollutants from aqueous solutions using biological material. The adsorption of copper, zinc and cadmium using two dried seaweeds Ecklonia maxima and Laminaria pallida (order Laminariales) and Kelpak waste (also made from Ecklonia maxima ), a byproduct from the manufacture of the seaweed concentrate Kelpak, were investigated under laboratory conditions, to determine some factors affecting heavy metal adsorption. Ion adsorption from single and mixed metal ion solutions of 10mgl − 1 and 100mgl − 1 containing copper, zinc and cadmium were tested at various temperatures and pH. Optimum adsorption occurred at pH 3 and pH 7 and Kelpak waste had equal or superior adsorption ability to dried Ecklonia maxima and Laminaria pallida , particularly for copper. Optimum adsorption occurred at temperatures of 20°C and 30°C. Heavy metal adsorption trends by the individual seaweed biosorbent remained constant regardless of the species of anion present. Drying of the experimental material (fan air and oven drying at 85°C) prior to adsorption cycles resulted in more efficient ion uptake, particularly after additional rehydration. Heavy metal uptake was monitored over a number of semi-continuous adsorption cycles, using the same biomasses. Ion uptake was the most efficient after 2–4 adsorption cycles.