## 1 Introduction  
The effluent produced by industrial or technological activity may contain high concentrations of heavy metals and the efficient treatment of these waste streams is of critical importance due to, in part, their toxic nature and, persistence in environment stemming from a lack of biodegradation pathways [1]. The release of Cu(II) has typically been the result of industrial activities such as electronics plating, wire drawing, copper polishing and so on, increasing the possibility to discharge copper into the water body [2]. In terms of human impact, the excessive ingestion of copper results in nausea vomiting and stomach cramps [3]. In general, the various technologies, such as biodegradation, photocatalysis, chemical precipitation, ion exchange, adsorption, filtration, reverse osmosis, have been developed and employed to eliminate heavy metal from water or wastewater [4]. Among them, chemical precipitation (CP), cation ion exchange (CIX) and adsorption were common technologies for Cu(II) removal [5; 6; 7]. Although each technology has advantages and disadvantages. The CP showed economic feasibility but huge sludge generation and CIX obtained high removal at a wide range solution pH but it required regeneration [8]. Adsorption is currently regarded as one of the most effective technologies for industrial wastewater treatment with a flexible design, ease of operation and effluent acceptable for release [9]. For example, activate carbon (AC) used in the granulated (GAC) or powdered (PAC) form, or iron-based oxides have been continuously studied due to their high sorption capacity and easy application in the field. However, they were only employed for the removal of anionic pollutants such as arsenic, phosphate and some organic matter in water and wastewater treatment. Alternatively, bio(ad)sorption has been recognized as a very promising process to remove heavy metals utilizing natural biopolymers, such as algae [10], alginate [2], chitin/chitosan, seaweed, and yeasts. This alternative sorption process offers substantial benefits including reduced toxicity of the materials, cost-effectiveness and high capacity [2]. Among them, alginate has been proved in heavy metal removal obtaining the high sorption capacity for Cu(II), chemical stability, and hydrophilicity [11; 12]. Alginate extracted from brown algae is a heteropolymer consisting of 1-4 linked \(\alpha\)-l-gluturonic and \(\beta\)-b-mannuronic acids [13]. The presence of carboxylic groups, naturally occurring in each constituent residue, showed high affinity for divalent cations, inducing complexation. Based on the acid-base and solubility properties, alginate has been employed to generate a variety of hydrogels after calcium (Ca(II)) crosslinking. Iron hydroxide or iron oxide, including granular iron hydroxide, has been widely applied in water/wastewater treatment to remove phosphate [14], arsenic [15], and Cr(VI) [16], which are present in an anionic form. The adsorption capacity of these materials is determined by the particle size, surface area, or pore volume. However, in order to be applied in the removal of cationic contaminants, the chemical modification of the surface is required. The methods, such as grafting [17] or coating [18] of inorganic materials, have shown to be effective in generating materials with increased selective sorption properties for cations but do so at the expense of the anion capacity due to the blockage of the sorption sites and/or pore volume. The layer of alginate on the surface of ferric hydroxide (FHO) can improve the cation sorption capacity by conducting the complex between Cu(II) and carboxyl groups. As result, the hybrid adsorbent (natural organic and inorganic mixed adsorbent) was used for arsenic removal using cellulose with iron oxyhydroxide [18] and iron oxide loaded alginate beads [19]. In principle, FHO has been applied for the removal of anions from the solution by the electrostatic interaction.