Uncontrolled release of acid mine drainage (AMD) causes widespread detrimental impacts on the receiving environment. Thus, effective treatment to neutralise AMD effluent pH and capture a suite of metals is required. In-situ hydrotalcite (HTC) precipitation is an emerging technology for AMD remediation. HTC has an inherent capacity to accommodate a range of cations and anions during in situ formation, offering a method of broad-spectrum contaminant removal. This study explored the feasibility of using seawater as an Mg source and synthetic AMD in HTC formation. The HTC was formed from a stoichiometric combination of synthetic AMD and seawater. While three initial stoichiometric M2+:M3+ ratios of 2:1, 3:1, and 4:1 were investigated, only HTC with an M2+:M3+ ratio of 2:1 was generated, as confirmed by both mineralogical and geochemical analyses. Importantly, the HTC was demonstrated to effectively remove a suite of metals present in AMD such as Cu, Zn, Al, and Mn with removal rates of between 99.97 to 99.99%. The HTC precipitate contained ≈6.6% Cu and 4.1% Zn, and thus shows the potential, if required, for future metal recovery. Since submarine placement is often used in metal mining and processing operations proximal to the coast, the stability of the HTC precipitate in seawater was also investigated. Importantly, only 0.2% of the Cu and 1.1% of the Zn within the HTC were subsequently leaching in decreasing increments into seawater over 30 days with decreasing increments after the initial seven days. This indicates robust element retention and confirms the potential of HTC for AMD remediation with direct submarine placement.

The overall objectives of the research were (1) to study the capability of sodium hydrosulfide (NaHS) and sulfidic natural water (SNW) of Sebau in recovery of Cu 2+ , (2) to investigate the potency of integrating treatments of neutralization with sulfidization using SNW of Sebau in removing Cu 2+ from acid mine drainage (AMD) collected from Batu Hijau site. The first objective was achieved by separately reacting (in situ) NaHS and SNW with a Cu 2+ solution at pH 5.5. The second objective was answered by conducting treatments of lime-neutralization by the use of three levels of pH (4.0; 5.5; 7.0) and sulfidization using SNW collected from Sebau, Lombok Island at three sampling points. The result showed that NaHS (61.6 mg/L) could precipitate Cu 2+ solution (44.45 mg/L) up to 71.3%, while SNW of Sebau could precipitate Cu 2+ solution (44.45 mg/L) for almost 100% at pH 5.5. The results also revealed that SNW could precipitate the remained Cu 2+ in the AMD from the neutralization treatment (pH 4 = 113.5 mg/L; pH 5.5 = 85.01 mg/L; and pH 7.0 = 2.372 mg/L) to 83.84% (pH = 4.0) and 100% (pH = 5.5 and 7.0). Although both pH 5.5 and 7.0 could completely precipitate Cu 2+ in the AMD, by comparing the experimental result with the stoichiometric analysis, it was predicted that pH 5.5 was an optimum pH level for the reaction between AMD and SNW to recover Cu 2+ in the AMD. Without neutralization treatment, SNW showed potentiality to recover Cu 2+ since the combination treatments of neutralization at pH 4 with SNW collected from three sample points resulted in a high percent recovery of Cu 2+ . ABSTRAKTujuan keseluruhan dari penelitian ini adalah: (1) untuk mempelajari kemampuan dari natrium hidrosulfida (NaHS) dan air belerang alami (SNW) dari Sebau dalam mengendapkan Cu 2+ , (2) untuk menginvestigasi potensi dari pengintegrasian perlakuan pada netralisasi dengan sulfidisasi menggunakan SNW dari Sebau dalam menghilangkan Cu 2+ terlarut yang berasal dari air asam tambang (AMD) dari Batu Hijau. Tujuan pertama telah tercapai dengan mereaksikan secara in situ NaHS dan SNW dengan larutan Cu 2+ secara terpisah pada pH 5,5. Tujuan kedua telah tercapai dengan melakukan perlakuan netralisasi dengan penggunakan tiga level pH (4, 5, 7) dan sulfidisasi menggunakan SNW yang diperoleh dari Sebau pada tiga titik sampel. Hasil menunjukkan bahwa NaHS (61,6 mg/L) dapat mengendapkan Cu 2+ (44,45 mg/L) sampai dengan 71,3%, sementara SNW dari Sebau dapat mengendapkan larutan Cu 2+ (44,45 mg/L) sampai dengan 100% pada pH 5,5. Hasil juga telah menunjukkan bahwa SNW dapat mengendapkan sisa Cu 2+ dalam AMD dari perlakuan netralisasi (pH 4 = 113,5 mg L; pH 5,5 = 85,01 mg /L; dan pH 7,0 = 2,372 mg/L) sampai dengan 83,84% (pH = 4) dan 100% (pH = 5,5 dan 7,0). Meskipun kedua pH 5,5 dan 7,0 dapat secara sempurna mengendapkan Cu 2+ dalam AMD, dengan membandingkan hasil eksperimen dengan analisis stoikiometri, diperkirakan bahwa pH 5,5 merupakan pH optimal untuk reaksi antara AMD dan SNW dalam mengendapkan Cu 2+ di dalam AMD. Tanpa perlakuan netralisasi,...