efficiency comparison of two types of almond shell in removal of mercury from aqueous solution

background: mercury is a heavy metal with high toxic effects. it has many apply to various industries, so can enter to the environment from different resources. therefore, its elimination from wastewater is a major challenge. in this study, removal of mercury from aqueous solution using two types of almond shell was investigated and compared. methods: this experimental-intervention study has been conducted in a batch method. at the beginning, the almond shell samples were collected and prepared. then the effect of parameters affecting the adsorption such as ph, the amount of sorbent, the initial ion concentration and contact time were investigated and optimized. at the end efficiency of two shells were compared using f-test and t-test. results: the most mercury removal was achieved at ph = 5.5± 0.1 in 10 min initial contact time. the obtained maximum adsorption capacity corresponding to langmuir isotherm model (for 5 and 7 gram per liter of sorbent) were 135/13 ± 8.34 and 105.30 ± 7.92 for hard and soft shell, respectively. difference was statistically significant (p= 0.0005). conclusion: although both of the adsorbents have high efficiency in removal of mercury from aqueous solution in comparison of other natural adsorbents but the result showed that mercury adsorption capacity by almond hard shell was more than almond soft shell. this sorbent as a simple, inexpensive, accessible, and without producing waste materials may proposed to industries which produce wastes including mercury.